Fair enough. I know Gadgetbridge lets you use some existing devices, but seems to lack in functionality and device coverage.
not any good ones that I found. At least compared to Strava/Training Peaks, which is what I use now.
Discussion
yeah it's pretty much all the off brand devices. anything worthwhile (imo) is not going to allow for that functionality. maybe one day. I do prefer garmin because they at least say they don't sell your personal data. Still collecting it, of course.