Great when it works. The actual app is good and responsive sometimes, but connecting and syncing i have issues. I have a fitbit sense and when its able to sync to my phone its usually good, during work outs the heart rate tracker does not keep up, and im sure to follow the instructions to wear the fitbit properly. But my biggest issue is the fitbit loosing sync with my mobile device espically over night and then the fitbit not being able to re-sync, i have to forget the fitbit in the app.