# Interval Timer for HIIT | Cero vs Relentless Coaching

The clearest difference is ads: Relentless Coaching at none against Interval Timer for HIIT | Cero's shown. Interval Timer for HIIT | Cero's advantage is update cadence (every 3 days vs every 2 months). On price, in-app purchases, device support and iOS requirement there is nothing between them.

Both are free to download. Interval Timer for HIIT | Cero sells 2 in-app purchases, starting at $2.99 per month and Relentless Coaching sells 1 in-app purchase, starting at $299.99 per month. Whichever you choose, the download price is not the number that matters.

Interval Timer for HIIT | Cero ships an update every 3 days, Relentless Coaching every 2 months. The most recent releases landed on October 29, 2026 and October 28, 2026 respectively.

## The numbers

| Metric | Interval Timer for HIIT | Cero | Relentless Coaching |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[4.7 (437 ratings)](https://appshunter.io/ios/app/interval-timer-for-hiit-cero/id1256319392/reviews)** | — |
| Number of ratings | **437** | — |
| Positive reviews | 74.6% of reviews | — |
| In-app purchases | Yes | Yes |
| Ads | Yes | **No** |
| Update frequency | **Every 3 days** | Every 2 months |
| Monetization | Free with in-app purchases | — |
| Size | 45 MB | 56 MB |
| Requires iOS | 16.0 | **15.0** |
| Devices | iPhone, iPad, Apple Watch | iPhone, iPad, iPod |
| Age rating | 4+ | 17+ |
| Developer | [Flawless Studio LLC](https://appshunter.io/developer/1228312508) | [James Lewis](https://appshunter.io/developer/1830497412) |

## What reviewers say

### Interval Timer for HIIT | Cero

[App page](https://appshunter.io/ios/app/interval-timer-for-hiit-cero/id1256319392)

This interval timer app enhances various workouts like HIIT, Tabata, and yoga with intuitive design and customizable timer modes. Create and save custom intervals, track calorie expenditure, and sync settings across devices, including Apple Watch.

**Highlights:** Customizable interval timers, Simple and advanced timer modes, Create and save multiple workout settings, Apple Watch compatibility with heart monitor, Automatic calorie tracking to Apple Health, Cross-device sync

**Features:** macOS Compatibility, Apple Watch app, Vision Pro support, iPhone Duo support

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Cero Pro Monthly | $2.99 | per month |
| Cero Pro | $14.99 | one-time |

**What reviewers like**

- 👍 Simple and straightforward
- 👍 Very practical and customizable
- 👍 Great for HIIT and Tabata
- 👍 Clear design and easy to use
- 👍 Good value, no subscription

**What reviewers complain about**

- 🔋 Drains battery
- 🎶 Music playback interrupted
- ⚠️ Ads interrupt timers
- 🔊 Weak or non-functional sound/haptics
- 🔄 Forced updates

**Reported bugs**

- App runs in background draining battery
- Rotation broke after update
- Apple workout app overrides Cero app on Apple Watch
- Interval signals too weak or not working

**Requested features**

- Ability to group timers
- Option to add warm-up and cool-down features
- Ability to type numbers for time adjustment
- Timer sounds through headphones or interrupting music
- Ability to change exercise names


### Relentless Coaching

[App page](https://appshunter.io/ios/app/relentless-coaching/id6749454399)

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

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| RELENTLESS ONLINE COACHING | $299.99 | per month |


## Frequently asked questions

### Is Interval Timer for HIIT | Cero free?

Interval Timer for HIIT | Cero is free to download, with in-app purchases available.

### Is Relentless Coaching free?

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

### Do Interval Timer for HIIT | Cero or Relentless Coaching have ads?

Interval Timer for HIIT | Cero shows ads; Relentless Coaching does not.

### Which is updated more often, Interval Timer for HIIT | Cero or Relentless Coaching?

Interval Timer for HIIT | Cero ships an update every 3 days, and Relentless Coaching every 2 months. Most recently, Interval Timer for HIIT | Cero was updated on October 29, 2026 and Relentless Coaching on October 28, 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.*