# FormKey vs SL Echo

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.

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.

## The numbers

| Metric | FormKey | SL Echo |
| --- | --- | --- |
| Price | **Free** | $6.99 |
| Rating | [4.5 (8 ratings)](https://appshunter.io/ios/app/formkey/id1535350561/reviews) | **[5.0 (1 ratings)](https://appshunter.io/ios/app/sl-echo/id6797348934/reviews)** |
| Number of ratings | **8** | 1 |
| Positive reviews | 57.1% of reviews | — |
| In-app purchases | Yes | **No** |
| Ads | No | No |
| Update frequency | Fortnightly | **Weekly** |
| Monetization | Paid | Paid |
| Size | 88 MB | 18 MB |
| Requires iOS | 18.6 | **15.0** |
| Devices | iPad | **iPhone, iPad, iPod** |
| Age rating | 4+ | 4+ |
| Developer | [Polyhedra](https://appshunter.io/developer/1535350563) | [VIACHESLAV ZHILTSOV](https://appshunter.io/developer/1862005860) |

## What reviewers say

### FormKey

[App page](https://appshunter.io/ios/app/formkey/id1535350561)

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.

**Highlights:** Shape-based note input, Color-coded octaves, Isomorphic key layout, Pattern recognition aid, Chord discovery assistance, Future update commitment

**Features:** Family Sharing, Vision Pro support

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| FormKey Full Unlock | $14.99 | one-time |


### SL Echo

[App page](https://appshunter.io/ios/app/sl-echo/id6797348934)

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.

**Highlights:** 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

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


## Frequently asked questions

### Is FormKey free?

FormKey is free to download, with in-app purchases available.

### Is SL Echo free?

SL Echo costs $6.99, with no in-app purchases.

### Which has better reviews, FormKey or SL Echo?

SL Echo is rated higher. FormKey averages 4.5 out of 5 from 8 ratings, while SL Echo averages 5.0 from 1 ratings.

### Do FormKey or SL Echo have ads?

Neither FormKey nor SL Echo shows ads.

### Which is updated more often, FormKey or SL Echo?

FormKey ships an update fortnightly, and SL Echo weekly. Most recently, FormKey was updated on October 24, 2026 and SL Echo on October 16, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*