This is one of the two mounts for rear lights that magic shine sells. This is the only one that is really worth it because the other one breaks every month or so because it’s incompatible with oval rails, or if your saddle mount pushes your rails apart too much. This one is perfect if you don’t touch it after the install. The rubber is super soft so if you clamp this in your work stand, it will break. If you remove and install too often, the rubber might give in.
Nice to have if have two two bike and one magicshine light easy to install and convenient to switch between two bikes