# HIIT Interval Timer | Cero vs Relentless Coaching

The clearest difference is ads: Relentless Coaching at none against HIIT Interval Timer | Cero's shown. HIIT Interval Timer | 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. HIIT Interval Timer | 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.

HIIT Interval Timer | Cero ships an update every 3 days, Relentless Coaching every 2 months. The most recent releases landed on October 16, 2026 and October 10, 2026 respectively.

## The numbers

| Metric | HIIT Interval Timer | Cero | Relentless Coaching |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[4.7 (435 ratings)](https://appshunter.io/ios/app/hiit-interval-timer-cero/id1256319392/reviews)** | — |
| Number of ratings | **435** | — |
| 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 | 42 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

### HIIT Interval Timer | Cero

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

**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 HIIT Interval Timer | Cero free?

HIIT Interval Timer | 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 HIIT Interval Timer | Cero or Relentless Coaching have ads?

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

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

HIIT Interval Timer | Cero ships an update every 3 days, and Relentless Coaching every 2 months. Most recently, HIIT Interval Timer | Cero was updated on October 16, 2026 and Relentless Coaching on October 10, 2026.

---

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