I have a couple of them, but they are the 3 lb single stage models. I use them in target-stye AR's, a 5.56 and a .308. So far no gripes about function.
They use itty-bitty C clips on the ends of the pins, which are easy to lose during installation and removal. They normally give you spares, and I would try to have some on hand.
I have a couple of 4 lb Timneys and think they are a little more robust, plus they are held in place with setscrews and can be easily removed & installed, without losing any tiny parts.
Last edited by tex_n_cal; 11/08/12. Reason: clarify