Review on Stay Safe And Visible Anytime With GPMTER Ultra Bright USB Rechargeable Bike Tail Light - Perfect For Road And Mountain Bikes by Steven Harmon

The lights are bright, so the 100 lumen (brightest mode) claim seems about right. They can be inserted into the mount at 90 degree angles, so you can mount vertically or horizontally regardless of orientate of the mounting strap. The mounting strap silicon is soft, making them easy to install. The light does not budge when mounted on my mountain bike seat stem. I've only done one ride on wet trails, and it survived. IDK yet how waterproof they are. For the money, they've exceeded my initial expectations.