The era of the over done M4 Carbine seems to be coming to an end, and I have already seen a transition towards the lighter weight Carbines.   When the M4 initially came out, it was suppose to be a lighter weight and smaller weapon to be wielded on the battle field, but many of the ones that I have seen on civilian firing ranges were about the same weight as an M1 Garand.   I have not had very good experience with using pressure switches on flashlights, not only have I seen them fail, like all other wired accessories, but they do open you up to the possibility of snagging on more things.   Something like that would get messed up in a wooded area and in close hallways ect. you can get it caught on just about anything that hangs out.

There is no real advice I can give about what to put on your firearm, all I can tell you to do is to think about the environment you are using it in and think about what “could happen” in that environment.   Streamlight flashlights have worked very well for me, I recently got some negative feedback from a fellow operator about the switches they have on the flashlights now, but I have avoided using pressure switches.   The Streamlight Scorpion I have on my M4 Carbines is located in such a position that I can reach it with my thumb and turn it on and off with ease.