I recently purchased a Garmin RTL510 (and Varia UT800) and paired them to my Garmin Fenix 5X watch and went for my first ride today. I didn't have the UT800 on but I did have the RTL510 on and could see it was working with my watch, but I seemed to have issues with the GPS functions of my watch, half the time it didn't record my speed and it took like 2 minutes to even start recording my starting point (when it always has synched to GPS immediately and not had an issue). In my garmin app it basically shows my speed for 1 minute, followed by a speed of 0 for another minute and then back to the actual speed and then back and forth. The Fenix 5X is listed as compatible with the RTL510 & UT800 so I don't see why it would be an issue. I am going to try and update the firmware on the RTL510 (if there is an update available) and try it out again tomorrow but was wondering if anyone has encountered anything similar.

I'm on the fence about getting a Garmin Edge bike computer since I already have a watch with most of the same functionality, but the larger display does seem appealing, I just wish they made basically an external display that would synch to my watch and not have all of the built in GPS sensors that I could just extend my display from my watch to, but I guess businesses are in business to make money, not offer me cheaper alternatives!