# Z21 vs Shelly BLE Debug

The clearest difference is rating: Z21 at 3.8 against Shelly BLE Debug's 3.0. Z21 also leads on update cadence (every 3 weeks vs every 2 months) and ratings volume (13 vs 2). Shelly BLE Debug's advantage is in-app purchases (none vs 1). On price, review sentiment, ads and device support there is nothing between them.

Both are free to download. Z21 sells 1 one-off in-app purchase. Shelly BLE Debug asks for nothing beyond the download.

Z21 holds the better App Store score, 3.8 against 3.0. That said, the two scores are not equally well evidenced: Z21 has 13 ratings behind it against 2, so its average is the more settled of the two. Written reviews complicate that: 38% of Z21's written reviews are positive against 42% of Shelly BLE Debug's, so the app with the better star average is not the one people write more warmly about.

Z21 ships an update every 3 weeks, Shelly BLE Debug every 2 months. The most recent releases landed on October 14, 2026 and October 9, 2026 respectively.

## The numbers

| Metric | Z21 | Shelly BLE Debug |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[3.8 (13 ratings)](https://appshunter.io/ios/app/z21/id1114706450/reviews)** | [3.0 (2 ratings)](https://appshunter.io/ios/app/shelly-ble-debug/id6449539118/reviews) |
| Number of ratings | **13** | 2 |
| Positive reviews | 38.3% of reviews | **41.7% of reviews** |
| In-app purchases | Yes | **No** |
| Ads | No | No |
| Update frequency | **Every 3 weeks** | Every 2 months |
| Monetization | Free with in-app purchases | **Free** |
| Size | 232 MB | 6 MB |
| Requires iOS | **12.0** | 15.0 |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [Modelleisenbahn GmbH](https://appshunter.io/developer/533805542) | [SHELLY EUROPE EOOD](https://appshunter.io/developer/1521653049) |

## What reviewers say

### Z21

[App page](https://appshunter.io/ios/app/z21/id1114706450)

Control your model train layout and locomotives wirelessly from your iOS device. Manage your locomotive library, program digital components, and operate switches and signals with an intuitive touch interface. Enjoy a realistic train control experience with customizable driver cabs.

**Highlights:** Wireless control of locomotives and layout, Manage locomotive library with images, Program digital components, Intuitive graphic interface for switches and signals, Downloadable driver cabs for realistic control, Demo mode available

**Features:** Family Sharing

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Z21 Full Version | $17.99 | one-time |

**What reviewers like**

- 👍 Intuitive and user-friendly interface
- 🚀 Fast and reliable locomotive control
- 💡 Innovative layout design with schematic control station
- 🎨 Clean, modern orange and black design
- 📱 Works seamlessly across multiple iOS devices

**What reviewers complain about**

- 🐛 Frequent app crashes and freezes
- 🔌 Connection drops to Z21 control station
- ⚠️ White screen startup issues in recent updates
- 🎮 Throttle display bugs showing incorrect speeds
- 📉 Slow performance on older devices

**Reported bugs**

- App crashes on startup (white screen issue)
- Connection drops to Z21 central station
- Throttle display shows incorrect or blank speeds
- Function buttons not responding properly in multitraction mode
- Route synchronization failures across multiple control station pages

**Requested features**

- Offline locomotive database access
- Dark mode or customizable color schemes
- Background image support for layout design
- Turntable/rotary module support
- Automatic event-based control (occupancy detection, crossing automation)


### Shelly BLE Debug

[App page](https://appshunter.io/ios/app/shelly-ble-debug/id6449539118)

Configure and manage Shelly Bluetooth Low Energy devices. Update firmware, pair your phone, and control beacon and buzzer functions. Easily locate your devices with this utility.

**Highlights:** Update device firmware, Pair device with phone, Turn beacon on/off, Control buzzer (if available), Locate device (if available)

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

**In-app purchases:** none


## Frequently asked questions

### Is Z21 free?

Z21 is free to download, with in-app purchases available.

### Is Shelly BLE Debug free?

Shelly BLE Debug is free to download, with no in-app purchases.

### Which has better reviews, Z21 or Shelly BLE Debug?

Z21 is rated higher. Z21 averages 3.8 out of 5 from 13 ratings, while Shelly BLE Debug averages 3.0 from 2 ratings.

### Do Z21 or Shelly BLE Debug have ads?

Neither Z21 nor Shelly BLE Debug shows ads.

### Which is updated more often, Z21 or Shelly BLE Debug?

Z21 ships an update every 3 weeks, and Shelly BLE Debug every 2 months. Most recently, Z21 was updated on October 14, 2026 and Shelly BLE Debug on October 9, 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.*