Garmin Varia is a GAME CHANGER. It's that good. I got mine about 2 weeks ago and can't imagine riding without it now.
A) It picks up vehicles behind you before you can hear them.
B) It tells you how MANY vehicles are behind you.
C) It has a special alert if one of those is coming up behind you at a fast speed.
D) The light blinks brighter and faster when the radar senses a vehicle. Most vehicles are now giving me 5' of space, on average, which is a HUGE difference from my regular blinking tail light that I used for the 13,500 miles of cycling I've done since I began 35 months ago.
E) 4 of my riding friends have bought one at my recommendation in the past 2 weeks. One of them called me after his first ride with it "just to thank you!"
I've not used a mirror or rear-facing camera so can't comment there... but the Varia is for REAL!
Gary