I've used a lot of different tail-lights over the years, and the Superflash beats them all. I've had mine since last spring, and use it commuting 3-4 days/week about 90 minutes each day. I generally run mine on steady mode, but use the flash mode when it's lighter outside. Batteries last a long time, even on steady mode. I've probably replaced the batteries twice or at most 3X since last spring. I don't ride much in the rain but haven't noticed any problems with my SF when I've been caught in the rain. You can mount it to your seat post, seat stays or clipped to your seatbag, helmet or jersey. Mine is mounted on my left seat stay because my seat bag is blocking my post.

The only tail-light that I am aware of that is brighter than the Superflash is the Dinotte. But it costs $150 or more and is difficult to mount unless you have a free seat post or a rear rack. My commute bike has neither, which I why I've steered away from the Dinotte.