I have the surefire x300 mounted on my glock 17. From time-to-time I will throw it on my AR. It is very bright and very durable. I have dropped it on multiple occasions and it works just like it should. If you have the cash, it is worth. However, if money is tight, I would recommend the Streamlight TLR.
Pros: Durable, Bright
Cons: Price
This review was written in the old system and had content requirements that are different than reviews written today.