Not sure about the USP but the P2000 and P2000sk internal lock is very easy to remove. Just pop the pin for the back-strap, slide it down and off the grip, and pluck the lock out with a small screwdriver (electronics or eyeglass).
There is a bitty little ball-bearing that retains it within the grip.
I used my P2000sk for a couple thousand rounds with the lock in place with no problems. It appears well designed, but I'm of the mind that I don't like the risk no matter how small.
The LEM is a light but sorta long double action pull.
The nice thing is that when you release the trigger for the next shot, you don't have to go all the way forward with the trigger (Short reset).
Matter of fact, I'll be selling mine as soon as I get my camera so's I can take some pics of it.
No locks whatsoever in her. Firing pin safety removed as well.
Rock solid.