# King vs ReadiSync by Fatigue Science

The clearest difference is device support: ReadiSync by Fatigue Science at 3 against King's 1. King's advantage is iOS requirement (9.0 vs 15.0). On price, update cadence, ads and in-app purchases there is nothing between them.

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

King ships an update every 2 months, ReadiSync by Fatigue Science monthly. The most recent releases landed on October 29, 2026 and October 26, 2026 respectively.

## The numbers

| Metric | King | ReadiSync by Fatigue Science |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[5.0 (2 ratings)](https://appshunter.io/ios/app/king-devick-test/id1033607954/reviews)** | — |
| Number of ratings | **2** | — |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 2 months | **Monthly** |
| Monetization | Free | — |
| Size | 243 MB | 66 MB |
| Requires iOS | **9.0** | 15.0 |
| Devices | iPad | **iPhone, iPad, iPod** |
| Age rating | 4+ | 4+ |
| Developer | [King-Devick Test, LLC](https://appshunter.io/developer/424793545) | [Fatigue Science](https://appshunter.io/developer/1042111871) |

## What reviewers say

### King

[App page](https://appshunter.io/ios/app/king-devick-test/id1033607954)

This app provides a quick and objective sideline concussion screening test for athletes. It helps identify potential concussions by assessing eye movements, attention, and concentration through a simple number-reading exercise. Requires an existing King-Devick Online account.

**Highlights:** Objective sideline concussion screening, Assess eye movements and attention, Administer baseline and post-injury tests, Works offline, Suitable for ages 5+

**Features:** macOS Compatibility

**In-app purchases:** none


### ReadiSync by Fatigue Science

[App page](https://appshunter.io/ios/app/readisync-by-fatigue-science/id1044418061)

**Features:** Vision Pro support

**In-app purchases:** none


## Frequently asked questions

### Is King free?

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

### Is ReadiSync by Fatigue Science free?

ReadiSync by Fatigue Science is free to download, with no in-app purchases.

### Do King or ReadiSync by Fatigue Science have ads?

Neither King nor ReadiSync by Fatigue Science shows ads.

### Which is updated more often, King or ReadiSync by Fatigue Science?

King ships an update every 2 months, and ReadiSync by Fatigue Science monthly. Most recently, King was updated on October 29, 2026 and ReadiSync by Fatigue Science on October 26, 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.*