Well i had my piranha in 99' and back then the sears on the piranha's had a defect and they blew. horrible after like 2 cases it would just turn into a shot gun. Before these your trigger pull would also be like 6 mm. After it woul only be like 5 :P .
This is a must unless you want an electro trigger. I give it a 7 because well it isn't perfect but it's above average. people go crazy with ratings. 5 is average and 10 is perfect. This is in between.