Plastic mounts are okay if they are designed properly. I have only had one light where the mount broke, and it was an inexpensive dyno light from amazon. Optics were good though. And it spent a lot of time in bike racks at work, so that probably didn't help. I also got a B&M dyno light from someone else that had a broken mount. I abuse mine, and they haven't broken. So this person was unlucky, I think.