Finally took the plunge after resisting for a couple of years, and moved from ANT+ Agent to Garmin Express. Painful experience. Only device to move (initially) was my FR610. This is how it went:
1. On adding device, got 'servers not available, cannot find serial number' error (it sees the ANT+ dongle, it sees the FR610, it knows it's a FR610, but cannot add it).
2. Second try was successful. Give my Garmin Connect credentials, device start synching, then... hangup. You can leave it here all night if you want, it's jammed.
3. Ok, kill GE, kill FR610, start all over, right? Nope. Now, GE does not see the FR610 anymore. It sees the ANT+ dongle, but nothing else.
4. Uninstall GE, install GE, start over: 'servers not available', again, yes, detected, Garmin Connect credentials, sync, ... hang. (obviously, the bug at #3 is in GE - reinstall fixes it, the FR610 status is unchanged).
5. Retry, this time flushing any activity left in the FR610. Same story (uninstall, install, detect, detect again, sync, hang)
6. Pray to suitable electronics gods, burn some incense, whatever - same. At this point GE uninstall/install adds a twist, you cannot reinstall unless you reboot the PC. Ah yes, sure.
7. Hard reset on FR610.
8. Restart GE (after reboot/install), detects, 'servers not available', detects, GC credentials, sync... success!!!!
9. Oh - there's a new firmware for the FR610 - the hard reset actually wipes firmware updates.
So - a few suggestions to the GE software team:
1. Fix the 'servers not available' bug.
2. A robust sync protocol between a PC and a wireless device needs a watchdog to monitor and kill the data transfer if it hangs.
3. Robust software survives a process kill/restart and does not get damaged to the point that a reinstall is needed to restore device detection capabilities
4. ... and even less get into rebooting to uninstall/reinstall the app...
5. ... and then can suggest 'hey, you have tried to connect this device 3 times so far, I've had to kill the data transfer every time, I recommend you hard-reset the device at this point'
This would have replaced a 1.5h ordeal by a 15 mins slightly complicated install. Just some suggestions.