The web site is both good and bad. There’s a lot of nice bits, but a lot of bugs. Though at least they can deliver British Statute measurements unlike Strava who have been asked to provide this for years and ignore us (i.e. C for temp, Miles for distance, feet for elevation etc, not bloody F for temp if you want miles and feet!).
Main annoyance with Connect site I find is the log in. I used Google to authenticate with but it sometimes forgets and then won’t pop up Google authenticate to re-authenticate. I can’t log in with the alternate credentials of email and password at all despite having it set up. Sometimes the login window just won’t pop up at all either. Terrible.
I do sync with Connect though despite using Strava as I don’t trust Strava either to not screw up or deny access to my raw data, plus connect gathers the full FIT file data with a lot more info. I can also use it to sync with some other service especially as I get increasingly frustrated with Strava’s lack of MTB awareness and concerned about privacy.
Connect app on Android is okay. My Garmin Edge 510 however is a pain to sync with the phone. It’s not Connect as I’ve had the same issue just doing basic Bluetooth pairing to the phone and to my old Windows phone, and older Android phone before that. There’s a trick to it though. Save the ride, shut down the Garmin, power on and activate Bluetooth on it and phone. It will pair that one time. Next ride you have to do it again.
And Garmin Express I never use since it was causing issues with some other apps on my PC. I just manually upload FIT files to Connect or use the Connect app on the phone.
Garmin firmware is also pretty bad. Never blindly accept a firmware update. I’ve had rides trashed due to that. Wait a long time until people are not reporting too many issues with that version. There’s a web updater from Garmin somewhere that you can manually update firmware too, instead of using Express which auto updates to the latest.