I have been working on a new mountain biking app for the last year called Hangtime. It is a free ride computer app that uses a smartphone's GPS, accelerometer, gyroscope, and altimeter to track a mountain bike ride. After recording a ride, the user can go back and see their performance in turns, jumps, climbs, etc. Below is a video that shows off some of the app's features.
https://youtu.be/TXiwzf-UJhQ
I wasn't sure I could get the performance required from Flutter/Dart vs. native as a one hour ride generates well over a million data points from all of the sensor data. However, performance has been more than adequate and the single code base has streamlined development.
If you want to give it a try, below are links to the app stores.
https://play.google.com/store/apps/details?id=com.rlued.hangtime
https://apps.apple.com/us/app/mtb-hangtime/id1516615267