I have had a FiveSeven for 8 months and it has been 100% reliable. It is the gun I carry when hiking/backpacking and I selected it specifically for that purpose. I chose it primarily due to light weight and high capacity which is a big plus for those activities. It is low recoil and easy to stay on target. It is expensive for a pistol and the ammo costs more than .223 but less than .45ACP.
I have no personal experience with the stopping power of the round. I freely admit to watching the pundit haters attack and the lovers defend the round. The truth is probably in the middle but, I do believe the real life evidence (i.e. - shootings that have occurred) that the 5.7x28 round is more effective than some would indicate. I certainly wouldn't want to be shot with it or anything else for that matter.