FormKey vs SL Echo
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
FormKey
This app is an intuitive MIDI controller that helps musicians improve by using shapes for notes and colors for octaves. Its unique isomorphic keys aid in pattern recognition and chord discovery, making music creation more accessible.
- Shape-based note input
- Color-coded octaves
- Isomorphic key layout
- Pattern recognition aid
- Chord discovery assistance
- Future update commitment
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Unlock your music potential. FormKey is the first music suite that helps you become the musician you've always imagined being, just by using it. INTRODUCING FORM Form is a new way to read and create music. Notes become shapes. Octaves become colors. Duration becomes a simple to read fraction. You can learn to read and play music in minutes. FormKey is the first release of the Form notation language, an open licensed music language designed to create instant music literacy. With the goal being to become a standard you'll see everywhere. THREE MODES: CREATE, LEARN, AND CONTROL • Create mode gives you a 16-track sequencer built on the classic drum machine workflow, modernized for today. Use your own AUv3 plugins or the three we built in to create full tracks from the ground up. • Learn lets you play and read your way through classical pieces while Form teaches you exactly what the music is doing, note by note. • Control turns FormKey into a MIDI controller for your external workflows, so it fits right into the setup you already have. THREE BRAND NEW AUv3 PLUGINS • Tone is a fully interactive subtractive synth that makes synthesis make sense. Every knob and connection is something you can hear and understand, so the architecture of a sound stops being a mystery. • Wave is a file-based sampler that lets you chop audio samples from your device, designed to make Slicing, and rearranging samples feel effortless instead of technical. • Patt3rn is a suite of modeled instruments curated to provide users with high quality options when looking for go to sounds every sequencer needs. • All 3 work in any host, so the instruments you learn in FormKey come with you wherever you go. SCALE MODE Reshape the keyboard to any of 26 scales, so every note you play stays in key. Choose from: • Major and minor: Major, Natural Minor, Melodic Minor, Harmonic Minor • Modes: Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian, Locrian • Pentatonic and blues: Major Pentatonic, Minor Pentatonic, Blues • Symmetric: Whole Tone, Whole-Half Diminished, Half-Whole Diminished, Augmented Hexatonic • World and exotic: Hungarian Minor, Neapolitan Minor, Byzantine, Enigmatic, Hirajoshi, In Sen, Kumoi, Iwato We've refined the interface across the app, making FormKey easier and more enjoyable to use. Every feature in FormKey is free to try. In celebration of our launch, $14.99 unlocks everything for the life of the app. We hope you love it as much as we do.
SL Echo
This audio effect app provides animated delay and space for musical decisions on iPad. Easily adjust time, feedback, and tone for various repeat styles, while maintaining a clear dry signal with stereo width and ducking. It supports AUv3 integration with popular music hosts.
- Animated delay and space effects
- Adjustable time and feedback
- Tone shaping controls
- Stereo width and ducking
- AUv3 support
- Standalone preview mode
- Factory and user presets
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SL Echo is a focused AUv3 delay effect designed for fast musical decisions on iPad. Move from a close vocal pocket to wide, evolving repeats without navigating complex pages. • Time and feedback for slapback or long trails • Tone shaping for darker or brighter repeats • Stereo width and ducking for a clear dry signal • Factory presets and local user presets • AUv3 support for compatible iPad music hosts Works as a standalone preview app and as an AUv3 effect in GarageBand, AUM, Cubasis, BeatMaker 3 and other compatible hosts.
Screenshots
Verdict
The clearest difference is price: FormKey at Free against SL Echo's $6.99. FormKey also leads on ratings volume (8 vs 1). SL Echo's advantage is rating (5.0 vs 4.5) and in-app purchases (none vs 1). On update cadence, ads and monetization model there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
FormKey is free to download; SL Echo costs $6.99 up front. FormKey sells 1 one-off in-app purchase. SL Echo asks for nothing beyond the download.
SL Echo holds the better App Store score, 5.0 against 4.5. That said, the two scores are not equally well evidenced: FormKey has 8 ratings behind it against 1, so its average is the more settled of the two.
FormKey ships an update fortnightly, SL Echo weekly. The most recent releases landed on October 24, 2026 and October 16, 2026 respectively.
| Parameter | FormKey | SL Echo |
|---|---|---|
| Price | Free — better | $6.99 |
| Rating | 4.5 (8 ratings) | 5.0 (1 ratings) — better |
| Positive reviews | 57.1% of reviews | — |
| Number of ratings | 8 — better | 1 |
| Update frequency | Fortnightly | Weekly — better |
| Ads | No | No |
| In-app purchases | Yes | No — better |
| Monetization | Paid | Paid |
| Devices | iPad | iPhone, iPad, iPod — better |
| Requires iOS | 18.6 | 15.0 — better |
| Further details — not scored | ||
| Size | 88 MB | 18 MB |
| Age rating | 4+ | 4+ |
| Developer | Polyhedra | VIACHESLAV ZHILTSOV |
Customer experience
FormKey
SL Echo
In-app purchases
FormKey
- FormKey Full Unlock$14.99
SL Echo
No in-app purchases









