I've had this for about a month now and ridden with it at least 20 times. While I wasn't sure I really needed it when I bought it, it has become almost a necessity now that I have used it. I am a senior rider (78 years), and it is wonderful having the few seconds of extra notification of a car approaching from behind. It gives one sound when a car is approaching, a slightly different sound when a string of cars is approaching, and a different sound if the approaching car turns off at another street before passing you. It also has a graphic display on the Element Bike Computer which changes color from green to orange to red as the car approaches. We have a lot of younger (almost everyone is younger than me now days) riders who are very capable (fast) including a fair number of pros (Boulder, Colorado), and the Trackr also alerts me when someone on our many bike trail is approaching on a bike. While I always double check with a mirror, this is a necessity at my age and probably useful for younger riders. The only issue I've found is riding a bikeway that parallels a highway (such as the one along US 36 from Boulder to Denver). The unit kind of goes crazy (constant beeping) in that situation and I have had to turn it off.
I'm not familiar with other, similar units ' although there are a few. I purchased this because of my experience with other Garmin products' and it was on sale! So far, I've not been disappointed as it does everything I'd hoped for. One thing I've noticed is that if using the screen on your phone, the traffic icons are spot on' as opposed to shutting the screen off and relying on the audio alert only: in this case, there could be two cars when you're expecting only one. That said, I still use my mirror to be sure. I also like the fact that you're given plenty of time before traffic comes near you' just in case you need to do some emergency maneuvering. If you're curious about radars, definitely check this one out!
BTW: I use an IPhone 12 with the Garmin Varia app. I understand it will also work with Ride with GPS, but I haven't tried that as yet.
This is my second Varia, bought for a bike I have in a different location. I've been using the first one for about three years now, and it is terrific. The new one is the same. The light itself is very bright, and the radar works well close to 100% of the time, even most of the time when riding in a paceline, but that is the occasional time when it won't pick up an approaching car because of interference from the back of the pack. Its range is excellent, picking up an approaching vehicle from about 1/4 mile back. Highly recommend.
This is one of those, 'didn't know how much I needed this,' purchases. The radar picks up cars further back than your ears can hear. I feel much more aware of what's behind me at all times. Can't imagine riding without it.
It works well with my Wahoo Bolt 2, though it doesn't remember my preferred flash settings (takes 15 seconds to configure pre-ride).
Battery life is fine. I can get several rides out of one charge if I'm only doing flash alerts. If I'm also using it as a persistent rear light it needs to be charged by the end of the ride.
Included seat post mount uses silicon bands to secure. Better clamp-based options out there.