The pairing with the radar sensor and the F6xPS is easy done. To pair as a light sensor didn’t work, but I think this wasn’t announced for the wearables (only for the edge series). The warnings are very accurate and there was no false alarm during my 2 hour bike trip. Cyclists traveling faster were also reliably displayed. Tried it also with the Varia app with my IPhone SE (2020) at the same time, was also working fine. One thing I have observed:
if you are driving on a narrow road and the car behind you has to brake because it cannot overtake due to the oncoming traffic etc., the radar signal for this car disappears (although it is still behind you) and only reappears when it accelerate. So you might forget this car for a moment and this could end in a dangerous situation...
Overall I am very satisfied with the combination varia rtl 516 and F6xPS.
I would like to have the possibility to use only the radar without the light (I have a good red light), this should save battery. I thought, I have read, that this is possible, but maybe only with the Varia rtl 515?