Your Apple Watch is! Check out how do I connect my Apple Watch to Fiit
Fiit is also compatible with 25 other fitness trackers (and counting!) Your Fitbit and other Garmins are not compatible — you can wear these devices but your performance won’t be tracked in Fiit.
If you want to track reps during strength training classes, you'll need the Fiit device which counts reps, as well as heart rate and calorie burn. Heart rate-only fitness trackers do not track reps.