# HIIT Interval Timer | Cero vs K2 (a514e2)

The clearest difference is in-app purchases: K2 (a514e2) at none against HIIT Interval Timer | Cero's 2. K2 (a514e2) also leads on ads (none vs shown). HIIT Interval Timer | Cero's advantage is device support (3 vs 1). On price, update cadence 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. K2 (a514e2) asks for nothing beyond the download.

HIIT Interval Timer | Cero ships an update every 3 days, K2 (a514e2) every 4 days. The most recent releases landed on October 16, 2026 and October 14, 2026 respectively.

## The numbers

| Metric | HIIT Interval Timer | Cero | K2 (a514e2) |
| --- | --- | --- |
| 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 | **No** |
| Ads | Yes | **No** |
| Update frequency | **Every 3 days** | Every 4 days |
| Monetization | Free with in-app purchases | — |
| Size | 42 MB | 53 MB |
| Requires iOS | **16.0** | 16.4 |
| Devices | **iPhone, iPad, Apple Watch** | iPhone |
| Age rating | 4+ | 4+ |
| Developer | [Flawless Studio LLC](https://appshunter.io/developer/1228312508) | [INVICTUS SPORT CENTER SOCIEDAD LIMITADA](https://appshunter.io/developer/1603598219) |

## 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


### K2 (a514e2)

[App page](https://appshunter.io/ios/app/k2-a514e2/id6809357838)

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

**In-app purchases:** none


## Frequently asked questions

### Is HIIT Interval Timer | Cero free?

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

### Is K2 (a514e2) free?

K2 (a514e2) is free to download, with no in-app purchases.

### Do HIIT Interval Timer | Cero or K2 (a514e2) have ads?

HIIT Interval Timer | Cero shows ads; K2 (a514e2) does not.

### Which is updated more often, HIIT Interval Timer | Cero or K2 (a514e2)?

HIIT Interval Timer | Cero ships an update every 3 days, and K2 (a514e2) every 4 days. Most recently, HIIT Interval Timer | Cero was updated on October 16, 2026 and K2 (a514e2) on October 14, 2026.

---

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