I knew about the Varia radar but I didn’t fully appreciate it until I was on a 6-day ride from Ottawa to Waterloo and my riding partner had one. It not only warned him of vehicles approaching from the rear, but the rapid flashing warned me riding behind him.
Even better, once paired, it displayed approaching cars on my Wahoo Element Bolt bike computer along with an audible warning. I didn’t know before now that it worked on the Wahoo, let alone that it would work for multiple riders!
He had his mounted on his helmet which, in my opinion, is much better than a seat post mount. It is higher up and more visible to vehicles, but also saves moving it among, in his case, 14 bikes. Harmon doesn’t provide helmet mounts, but it is not difficult to jury-rig with zip ties on many helmets.
Here is a photo of mine:
What I love most about the Varia is the peace of mind and relaxation it provides when riding on quiet country roads. It is less useful on busy roads where the frequent alerts provide no real information.
In terms of accuracy, we got a few false positives but I did not notice any false negatives— which is the way you want it on a safety device.
I got mine, in stock, from Ziggy’s for just over $300
