I have been riding for 10 rides with them and only regret I haven't bought earlier. I don't understand why is not everyone using them.
I was in a bit of doubt because of dioptric insert but the frame is surprisingly nowhere near in the field of view and the mirror marked as Medium size is more than enough.
Sun glares only happen under very specific angle of head and sun, not a real issue. Mirror is once set and forget, I don't need further adjustments.
Field of view is comparable to a car but by using your head as a gun pointer you can glare over entire space behind you in a second.
Selling point is peace in mind and ensurement before every significant maneuver. FOV is restricted minimally, just when connecting to the main road from the right you need to be aware you have mirror blocking it there so you should tilt your head a bit down.
It's quite addictive so you should still be aware of what's going on in the front of you. On the other hand I sometimes slip with my attention and catch myself checking my back, then the time passes quicker and I don't get easily bored.
Compared to Garmin Varia radar, it's active but it gives you more information about your surrounding.
The added safety is not in the fact that you know the car is there, but from the fact that you can mentally prepare for it passing you along in roughly that much time, in that speed, in that distance from you, and when you're prepared you significantly lower the risk of any collision. And even more importantly, you reduce your neck tilt so you don't get so fratiqued from looking back.
The dioptric "sandwich" holds on your head surprisingly firmly, glasses haven't ever slipped down.
100% recommend.