bought a Garmin Varia RTL 515, loved it, had to send it back for warranty, the usb cover got dislodged on gravel ride. Did not want to be without a radar so I got a Magene L508 in the interim. Now have two radar lights and I ride with the Magene and lend the Garmin to friends to convince them to buy their own (and the end up buying the Magene).
Main differences other that Magene is smart tail light and brightens when you brake (which is why I ride with it)
The Garmin is slightly brighter (but I run both in flashing mode)
When a car matches your speed, the Garmin will keep the alert for a couple of seconds longer than the Magene before it drops. But once a car or other object including another bike matches your speed the alert will disappear.
Other than that the are the same, get false postives from both, usually from vehicles traveling in the opposite direction. Never had a false negative, ie no missed approaching cars. They both work with Wahoo Bolt V2, Wahoo Elmnt, Garmin 510, Garmin 935 watch and Magene C 508.