I hadn't considered this until I had trouble with cars on faster descents. The RADAR works just as I expected, and gives me enough warning time to look ahead on the road and choose where to bike, and to turn and take a look behind me. This is what I wanted, a reliable device that told when to look. I'd recommend this rear light for anyone.
As an owner of the original Varia, my only real complaint was battery life. Version 2 has fixed that. The original was good for 4-4.5 hrs, I have yet to come even close to draining the battery on my new model. Might be a tad heavier (I haven't weighed it) but well worth the tradeoff!
Likes the included mount fits on my pinarello aero seat post. It's fairly small but still very bright. It changes flash patterns and intensity when cars approach. It works seamlessly with my garmin 520 head unit. I ride with a small mirror on my glasses but this gives me MUCH earlier warning for approaching cars (and I'm not always staring at my mirror either). The radar works fabulously on smaller, more lightly traveled roads where you may not hear a car till the last minute. I find the display very easy to interpret. The form factor of the this model varia is nicer sleeker than the original model and works just as well.
Dislikes the seat mount is just a rubber band with a standard garmin quarter twist mount. The twist part feels very secure to me but the actual assembly tends to rotate on the seat post from time to time. It's an easy fix, even while riding but I'm not always paying attention. Getting it to pair the first time was a little dodgy (if I recall, I had to pair the radar and then also include it as part of a garmin light network, but it was only a one time issue)
Overall I now consider this to be an essential part of my daily riding gear.