I used to rely on handlebar mirrors and/or quick glances over my shoulder to check for cars behind me, but the Garmin Varia has been a savior and at least replaced the mirrors. The read out display on my Garmin head unit gives and audible warning and also provides ample alert to cars approaching from the rear. If there is any concern it is that while in group rides with teammates behind me the radar can sometimes confuse cars and bikes and filter out the warning, but perhaps I don't have the unit set correctly to accommodate for both bikes and cars behind me. I will not ride again without the Varia on my bike and should have purchased it when it first came out.
They should probably take "lightweight" out of the light description. The weight is my greatest complaint about the light. I like that it sits underneath the garmin computer. I primarily use it as a daytime flashing light and it's very effective for that purpose. It is plenty bright enough for later this year when I start riding an hour before sun up to avoid the Arizona heat. Attaching the light to the garmin out front holder took a little getting used to but overall it's no problem.
I don't see anything not to like about this light. It's built like a tank. The mount is strong. It's rechargeable and it has a red read out on top that shows you how much charge time that is left in the light. It also has a memory on it that lets say that you are only using the high/medium beams. It remembers that and lights up those 2 settings. I can see me getting a lot of quality use out of this light. Use it mainly for night gravel riding.
Bought this light because the reviews online were solid, and importantly, it seamlessly mounts on the same Garmin Out Front mount (included in Varia box) that my Garmin 1030 bike computer does. The light performs exactly as it is advertised with multiple modes to accommodate both low light and daylight conditions. I mostly ride a high end road bike in daylight conditions on suburban roads, so the bright, flashing daylight mode is perfect to grab the attention of boneheaded motorists approaching me. Have only had the light for less than a month and roughly 15 hours of outdoor riding, but it has yet to need recharging, and is still throwing out intense light on the daylight flashing mode. The only issue that I have had with the the light is that it does not seem to pair with my Garmin 1030 as expected. Not a big deal, because I really only wanted the daylight flasher and Garmin Out Front mount option anyway.