Just recently received this unit. I have it paired with the 520 plus. It seems to work well. However I cannot do the firmware update from 3.2 to 3.3. Aug 8 I called Garmin support and was on the phone with them for over 30 minutes and no resolution. There is now an open help ticket on this but I have heard nothing back from Garmin. Will advise when I do. I sent them a follow-up this morning.
Anyone have luck on doing the firmware update?
Note: See the same issue referenced by stevereid in this topic - https://forums.garmin.com/forum/into-sports/cycling/varia/1389948-vari-radar-rtl510-connected-to-edge-520