I gave this a two only because when it does work it's bright and attaches to my bike ok.
If I don't charge it before I ride it doesn't work. Sometimes it just doesn't plain work at all. Very disappointed and would not recommend this. I would rate this light as extremely unreliable.
Just such a smart design. The onoff switch is the lens, just tap it twice. And to select another light mode is also the lens, just tap it once. USB rechargeable, but the smartest thing about this light that it is angled, so once you tighten the rubber band around your set post it will shine backwards, and not down to the ground light most other taillights will do. Also lightweight and you won't run out of battery soon with the 35 hour runtime.
Wildly simple to attach, move and use. Charged it once two weeks ago, haven't had to charge it yet. Simple operation (I often forget to start it before the ride, easy to simply reach down and double-tap the lens to get it going). Only improvement I could ask for is a slower flash mode - the flash mode lasts forever, but it's a little frenetic for anyone following. Slower-paced flash would be great. Still a great product.
Can't ask for more in a taillight. I can use it for two hours a day for at least 2 weeks without having to charge. This is perfect. Super easy to swap between bikes too. I put it on my wishbone seat stay or bridging two normal seat stays.
I commute year-around and in the winter it is completely dark on the way home. I like to have two independent tail lights in case one goes out along the way. It is lightweight, easily attaches securely to the seat post and has been trouble free half way through the winter. I'm not sure one of these is bright enough for night riding on roads with speed limits exceeding 30 MPH hence the four star rating instead of five.
Not the brightest on the market, but perfectly adequate. Lightweight and fits on seatpost. I am 5'4 so have limited real estate on seatpost, but this light is visible, not obstructed by seatbag either.