# N4x4 vs VO2 Flow

The clearest difference is in-app purchases: N4x4 at none against VO2 Flow's 1. N4x4 also leads on ads (none vs shown) and update cadence (every 2 days vs every 5 weeks). VO2 Flow's advantage is rating (5.0 vs 4.5) and iOS requirement (13.0 vs 17.5). On price and device support there is nothing between them.

Both are free to download. VO2 Flow sells 1 one-off in-app purchase. N4x4 asks for nothing beyond the download.

VO2 Flow holds the better App Store score, 5.0 against 4.5. That said, the two scores are not equally well evidenced: N4x4 has 20 ratings behind it against 1, so its average is the more settled of the two.

N4x4 ships an update every 2 days, VO2 Flow every 5 weeks. The most recent releases landed on November 4, 2026 and October 30, 2026 respectively.

## The numbers

| Metric | N4x4 | VO2 Flow |
| --- | --- | --- |
| Price | Free | Free |
| Rating | [4.5 (20 ratings)](https://appshunter.io/ios/app/n4x4/id6686407796/reviews) | **[5.0 (1 ratings)](https://appshunter.io/ios/app/vo2-flow-norwegian-4x4-timer/id6757104585/reviews)** |
| Number of ratings | **20** | 1 |
| Positive reviews | 66.7% of reviews | — |
| In-app purchases | **No** | Yes |
| Ads | **No** | Yes |
| Update frequency | **Every 2 days** | Every 5 weeks |
| Monetization | **Free** | Free with in-app purchases |
| Size | 16 MB | 25 MB |
| Requires iOS | 17.5 | **13.0** |
| Devices | iPhone, Apple Watch | **iPhone, iPad, iPod** |
| Age rating | 4+ | 4+ |
| Developer | [Jan van Rensburg](https://appshunter.io/developer/1688121173) | [CHRISTOPHER DISCOTTO](https://appshunter.io/developer/1864553330) |

## What reviewers say

### N4x4

[App page](https://appshunter.io/ios/app/n4x4/id6686407796)

This app guides you through high-intensity interval training to improve VO2 max. It uses your heart rate monitor to provide real-time cues for effort and recovery, tracking your progress over time. The app offers voice coaching and reminders to help you build a consistent training habit.

**Highlights:** Real-time heart rate zone guidance, Voice and haptic interval cues, Supports multiple heart rate monitors, Workout progress tracking, Hands-free training mode, Apple Health integration

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

**In-app purchases:** none


### VO2 Flow

[App page](https://appshunter.io/ios/app/vo2-flow-norwegian-4x4-timer/id6757104585)

This interval training app guides you through the Norwegian 4x4 protocol or allows you to create custom workout routines. It offers audio cues, haptic feedback, and music integration to enhance your training sessions. Track your progress with workout history and unlock achievements.

**Highlights:** Norwegian 4x4 protocol, Custom interval creation, Workout history tracking, Apple Music integration, Audio cues and haptic feedback, Achievement badges

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

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Pro Upgrade | $4.99 | one-time |


## Frequently asked questions

### Is N4x4 free?

N4x4 is free to download, with no in-app purchases.

### Is VO2 Flow free?

VO2 Flow is free to download, with in-app purchases available.

### Which has better reviews, N4x4 or VO2 Flow?

VO2 Flow is rated higher. N4x4 averages 4.5 out of 5 from 20 ratings, while VO2 Flow averages 5.0 from 1 ratings.

### Do N4x4 or VO2 Flow have ads?

VO2 Flow shows ads; N4x4 does not.

### Which is updated more often, N4x4 or VO2 Flow?

N4x4 ships an update every 2 days, and VO2 Flow every 5 weeks. Most recently, N4x4 was updated on November 4, 2026 and VO2 Flow on October 30, 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.*