# XOSS vs FitFly(US)

The clearest difference is rating: XOSS at 4.4 against FitFly(US)'s 3.1. XOSS also leads on review sentiment (52% vs 13%) and ratings volume (399 vs 86). FitFly(US)'s advantage is iOS requirement (10.0 vs 18). 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.

XOSS holds the better App Store score, 4.4 against 3.1. Both are backed by a comparable volume of ratings — 399 and 86 respectively. Written reviews point the same way: 52% of XOSS's written reviews are positive against 13% of FitFly(US)'s.

XOSS ships an update every 6 weeks, FitFly(US) monthly. The most recent releases landed on November 6, 2026 and November 3, 2026 respectively.

## The numbers

| Metric | XOSS | FitFly(US) |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[4.4 (399 ratings)](https://appshunter.io/ios/app/xoss-train-with-science/id1267749721/reviews)** | [3.1 (86 ratings)](https://appshunter.io/ios/app/fitflyus/id1505971648/reviews) |
| Number of ratings | **399** | 86 |
| Positive reviews | **52.3% of reviews** | 13.3% of reviews |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 6 weeks | **Monthly** |
| Monetization | Free | Free |
| Size | 110 MB | 45 MB |
| Requires iOS | 18 | **10.0** |
| Devices | iPhone | **iPhone, iPod** |
| Age rating | 4+ | 4+ |
| Developer | [XOSS HONG KONG CO., LIMITED](https://appshunter.io/developer/1530144728) | [琳 陈](https://appshunter.io/developer/1528936465) |

## What reviewers say

### XOSS

[App page](https://appshunter.io/ios/app/xoss-train-with-science/id1267749721)

Record and analyze your outdoor sports activities with detailed metrics like speed, cadence, and heart rate. Plan routes, sync data from various bike computers, and share your progress with friends. Offers advanced data analysis with charts and GPS tracking.

**Highlights:** Syncs with bike computers, Records workout data, Advanced data analysis, GPS tracking on map, Route planning, Syncs with Strava/TrainingPeaks

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

**In-app purchases:** none

**What reviewers like**

- 👍 Clean and simple interface
- 🚀 Reliable data tracking
- 💡 Useful 3D route visualization
- 🤝 Seamless Strava integration
- 💰 Good value for money

**What reviewers complain about**

- 🐛 Inconsistent GPS connectivity
- 🔄 Sync issues with Strava
- 🔍 Limited data analytics
- 🌐 Lack of language options (e.g. French, Russian)
- 🔋 Battery drain concerns

**Reported bugs**

- App crashes after recent updates
- Unable to update device firmware on iOS
- Sensor connectivity problems
- Incorrect distance/speed measurements

**Requested features**

- Add more detailed metrics (e.g. elevation, power)
- Improve route editing and privacy controls
- Introduce automatic sync options
- Provide more comprehensive data export capabilities


### FitFly(US)

[App page](https://appshunter.io/ios/app/fitflyus/id1505971648)

Accurately record various fitness activities like running, cycling, and walking. Get multi-dimensional body state evaluations and professional physiological indexes to make your fitness journey more scientific and effective. Enjoy playback of your fitness records and synchronize data with Apple Health.

**Highlights:** Accurate fitness activity recording, Multi-dimensional body state evaluation, Professional physiological indexes, Exercise track record and playback, Apple Health data synchronization

**Features:** macOS Compatibility

**In-app purchases:** none

**What reviewers like**

- 👍 Looks and fits well
- 👍 Works perfectly (after update)
- 👍 Connects very well
- 👍 Good for the price point

**What reviewers complain about**

- 🐛 Cannot convert units (C to F, cm to in)
- 🐛 Useless/Not working
- 🐛 Cannot sync contacts, messages, weather
- 🐛 App is useless, never stays connected
- 🐛 Health items not tracked

**Reported bugs**

- Cannot convert units (C to F, cm to in)
- App is useless, never stays connected
- Steps not cumulative
- Cannot upload photos to watch screen after update
- Gesture wake up doesn't work after connecting to app

**Requested features**

- Convert units (Celsius to Fahrenheit, centimeters to inches)
- More customization options for wallpapers/themes
- Add Persian language support
- Improve app connectivity and stability
- Enable cumulative step tracking


## Frequently asked questions

### Is XOSS free?

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

### Is FitFly(US) free?

FitFly(US) is free to download, with no in-app purchases.

### Which has better reviews, XOSS or FitFly(US)?

XOSS is rated higher. XOSS averages 4.4 out of 5 from 399 ratings, while FitFly(US) averages 3.1 from 86 ratings.

### Do XOSS or FitFly(US) have ads?

Neither XOSS nor FitFly(US) shows ads.

### Which is updated more often, XOSS or FitFly(US)?

XOSS ships an update every 6 weeks, and FitFly(US) monthly. Most recently, XOSS was updated on November 6, 2026 and FitFly(US) on November 3, 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.*