Guides · Tennis
Tennis swing trainer vs app: Dragonet, SLAP FLAP, magnetic sticks and ShadowSwing
The short answer. Click and magnetic swing trainers and the ShadowSwing app reward the same thing: a loose arm and a racket head that speeds up through contact. A stick wins on real weight, feel in the hand and having no phone to hold. The app wins on padel and pickleball modes, speed numbers, 3D replay and guided workouts, and you don't have to buy anything to start. Neither replaces hitting balls.
What these trainers actually reward
Every device on this page is built around the release. On a good groundstroke or serve, the racket head speeds up late, the wrist stays soft, and the fastest part of the swing arrives around contact rather than at the start. A tight, pushed swing doesn't do that, and none of these tools will reward it.
The Dragonet Swing does it with a moving internal mass that clicks at peak acceleration. Magnetic trainers snap when the swing is fast and fluid enough. SLAP FLAP clips onto your racket and makes a sound on a low-to-high forward swing. ShadowSwing plays the ball sound only once the racket head is moving fast enough.
In his Dragonet Swing review, the Feel Tennis coach says the device can help players "create better wrist lag" and "feel where acceleration should happen". He's also clear about the limit: it "does not teach reading the ball, spacing, movement, or adjustment steps."
One more caveat. Modern topspin groundstrokes involve a lot of brushing up the back of the ball, and a click or a sound can't tell you anything about swing path or spin. These tools train the release. For the rest, see Shadow swings: drills for every stroke, and whether they work.
The trainers
Dragonet Swing
A fully mechanical trainer made in Italy. Dragonet says it's "100% mechanical, with no electronics or sensors": a mass slides inside the tube and strikes a stop at peak acceleration, giving an audible click, and the maker says the "sound intensity reflects swing speed". Weight adjusts from 390 g to 474 g with snap-in micro-weights (5 × 17 g) at the head or butt, and there are two airflow resistance levels, light and high. The kit includes the device, five micro-weights, a gasket, two overgrips and a quick-start guide. Dragonet lists forehand, backhand, serve, volley and smash.
Price as shown on dragonet.it on 16 October 2026: €179.00, tax included. (Dragonet also makes ball machines. They're a separate product.)
The Feel Tennis verdict: heavier than a racket, "a very good warm-up tool", and "not for beginners". He positions it for players around 3.5 and up as a refinement tool, and warns that a high resistance setting can push players into muscling the click. He discloses that he received the device free of charge and may earn a commission through his link.
SLAP FLAP
A clip that turns your own racket into a trainer. SLAP FLAP describes a "two-sound feedback system": the first sound comes during the low-to-high forward swing, the second at the finish and reset. It's designed only for shadow swings, and the maker says to "always remove SLAP FLAP before hitting balls". It recommends 10 to 15 minutes a day, and its FAQ says it complements coaching rather than replacing it.
Price as shown on slapflap.com on 16 October 2026: $49.99 USD on sale (regular $59.99 USD).
Magnetic trainers
Magnetic sticks use magnetic resistance and snap when the swing is fast and fluid enough. Many brands sell them. As one example, the Swng Pro page lists an "audible snap", a resistance dial ("Five levels"), a real racket-style grip, "No setup, no app" and a 15-day swing program, and says it trains all four strokes.
Price as shown on swnglab.com on 16 October 2026: $89.00 USD (shown against a crossed-out $179.00).
ShadowSwing (the app behind this site)
An app for iPhone and Android. You hold the phone like the grip, and in Free Hitting the ball sound plays only once the racket head is moving fast enough. More in where the app is better.
Comparison table
| Dragonet Swing | SLAP FLAP | Magnetic trainer (e.g. Swng Pro) | ShadowSwing app | |
|---|---|---|---|---|
| Price (as shown, 16 Oct 2026) | €179.00, tax included | $49.99 USD (regular $59.99) | $89.00 USD | Free to download, no account; Pro $39.99/yr |
| What you hold | Its own handle, 390 to 474 g | Your own racket with the clip | Its own handle with a racket-style grip | Your phone, held like the grip |
| Feedback | Mechanical click; maker says intensity reflects speed | Two sounds (forward swing, finish) | Magnetic snap | Ball sound once racket-head speed is high enough |
| Adjustable | Weight, balance, 2 resistance levels | Not stated | Resistance dial | Workouts and modes |
| Sports and strokes listed | Tennis: forehand, backhand, serve, volley, smash | Tennis | Tennis: all four strokes | Tennis, padel, pickleball |
| Numbers | No (no electronics) | No | No ("no app") | Racket-head speed per swing (Pro), swing count |
| Replay | No | No | No | 3D stroke replay |
| Guided practice | Quick-start guide | 10 to 15 min a day recommended | 15-day swing program | Coach-voice workouts |
| Needs | Nothing else | A racket | Nothing else | A phone |
| Hit balls with it | Not stated | No (remove it first) | Not stated | No (shadow swings only) |
Prices and features from each maker's page on 16 October 2026. Prices change, so check before you buy. We make ShadowSwing.
What a stick does better
Real weight in the hand. A phone weighs far less than a racket. Dragonet lets you set the mass and balance, and the Feel Tennis review likes it as a warm-up exactly because it's heavier than a racket, so your own racket feels lighter afterwards.
A proper grip. Dragonet ships with overgrips, the Swng Pro page describes a racket-style grip, and SLAP FLAP uses your actual racket. Holding a phone like a grip is a reasonable stand-in for the release. It isn't the same feel.
No phone to hold or drop. A stick can't fly out of your hand and crack a screen, and it doesn't need a charge. That matters on a full-speed serve.
Ready in the bag. Mechanical sticks need no battery and no screen, so they're easy to use as a warm-up before a match.
Your own racket, with SLAP FLAP. If you want the feedback on the exact frame you play with, it's the only option here that does that.
Where the app is better
Padel and pickleball. ShadowSwing has separate tennis, padel and pickleball modes, each with its own ball sound and swing sensitivity. The sticks above are sold as tennis trainers.
Numbers. With Pro, ShadowSwing shows racket-head speed on every swing and keeps a speed trend per sport. Every swing is counted, and a daily goal ring fills as you practice.
Replay. Shot Analysis replays a single forehand, backhand, serve or volley on a 3D court, showing the path the racket head traveled and where the string face was pointing. You can orbit it and slow it down. It shows you the path; it doesn't judge whether that path is right.
Guided workouts. A coach voice calls the strokes, counts the reps and times the rests. Pro users can build their own.
Nothing to buy. It's free to download, no account, and Pro is $39.99 a year. It runs on iPhone and Android.
What it can't do: it doesn't watch your body, so it can't check your grip, stance, footwork, contact point, swing path or spin, and it doesn't see a ball. If you want video of your stroke, read Do you need a camera to practice your swing at home?, and for the wider field, see Best tennis training apps in 2026: an honest comparison.
Who should buy what
| You are | Best fit |
|---|---|
| A beginner below about 3.0 | Not a stick yet. The Feel Tennis review says beginners need basic stroke organization first. Start with shadow swings and a coach's cues, a wall, or the app (free to download). |
| A club player around 3.5+ refining the release | A stick is worth considering. |
| A padel or pickleball player | The app. The sticks here are tennis trainers. |
| Someone who wants numbers or a replay | The app. None of the sticks has electronics. |
| Someone who hates holding a phone and wants weight for a warm-up | A stick, with Dragonet for adjustable weight or SLAP FLAP for your own racket. |
| Curious about both | Both is fine. They train the same cue. |
Using them together
They don't compete as much as the table suggests. A sensible split: use the stick for a few minutes before you play, when the extra weight wakes the arm up, and use the app on days off court, when a workout with a coach voice and a swing count keeps the reps honest. The cue is the same for both, a loose arm and a racket head that arrives late and fast. If the stick clicks and the app sound fires, you're doing the same thing right twice.
Questions
Is a tennis swing trainer worth it?
It can be, for one job: feeling a loose, late release of the racket head. Click and magnetic trainers give instant feedback on that, and the Feel Tennis review calls the Dragonet "a very good warm-up tool". They don't teach footwork, spacing or reading the ball, and the same reviewer suggests they suit players around 3.5 and up rather than beginners.
What does the Dragonet Swing do? (Dragonet Swing review summary)
The Dragonet Swing is a mechanical tennis trainer with an internal mass that clicks at peak acceleration. Its maker says the click gets louder with swing speed, and that weight (390 to 474 g) and resistance are adjustable. It costs €179.00, tax included, on the official site (checked 16 October 2026).
Can a phone app replace a swing trainer?
Partly. ShadowSwing, which we make, rewards the same release: you hold your phone like the grip, and the ball sound plays only once the racket head moves fast enough. It adds speed numbers, 3D replay, workouts and padel and pickleball modes, but it has no real racket weight in the hand.
What's the difference between SLAP FLAP and Dragonet?
SLAP FLAP clips onto your own racket and gives two sounds, one on a low-to-high forward swing and one at the finish. The Dragonet Swing is a separate, heavier handle with a mechanical click and adjustable weight and resistance. On their official pages on 16 October 2026, SLAP FLAP showed $49.99 USD and Dragonet €179.00.
Are swing trainers good for beginners?
Usually not as the first step. The Feel Tennis Dragonet review says players below about 3.0 should build basic stroke organization first, and that the trainer can reinforce an arm-only swing. Beginners get more from shadow swings with a coach's cues, a wall, and plenty of balls.
Is there a swing trainer for padel or pickleball?
The click and magnetic trainers here are sold for tennis. ShadowSwing has padel and pickleball modes with their own sounds, so you can shadow a bandeja or a pickleball serve with your phone. See Padel training at home: drills without a court and Pickleball practice at home: drills without a court.
Do swing trainers replace hitting balls?
No. The review linked here is clear on this: timing, spacing and decision-making need real balls. Trainers and apps are for reps between sessions and for warm-ups. For solo ball work, see How to practice tennis alone, without a partner.