I have one. I just bought it to reduce frame wear because my P99 QA is my first plastic gun and I am nervous (yes I know it is silly) about plastic guns. IMO it has has a bit too much tension in the mainspring (it also has a subspring). Much greater than the factory spec. I am going to write Springco and ask them about buy a new spring so I can cut it down or see if they can sell me a cut down one.
Other than that, I have shot thousands of many types and brands of rounds with it with zero problems. It is however a slight pain to get back in after taking it out (not really a big deal). You will notice that the factory plastic unit flexes a bit; the Springco device is solid metal and does not flex when the slide is off the gun so I have to snag it with a finger and push down to get the rod to allign.