They suck (tend to break easily) and DO NOT WORK WHEN FIRING FULL AUTO!!!!!! (or shooting in single mode really fast)
Don't and instead replace the spring to something more reasonable. I notice you list your location as Calgary, if you're thinking of playing at Trek (only place I can think of that you'd probably need one) then ask first but be prepared for a possible no since the elastic thing that you put in the velocity reducer does break from time to time and using a hot gun like a Kraken (which I believe OOTB is something like 370) is no fun for the person on the other end when you're playing in such tight quarters.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE