Works as described and cut just right to fit in my retaliator. I really recommend this spring. It's really powerful but not too much to where you can even pull the slide back like the 12kg spring. (To be fair that spring is meant for really strong people).If you cant figure out how to get the spring in because its so strong, put the spring in the retaliator to where it is still sticking out of the back, then close the shell but not all the way so you have room to push the spring in from the back. That is the easiest way to do it.
The power increase is significant, and the install should be fairly straightforward if you've modded a blaster before. It does make the prime fairly uncomfortable over prolonged use, so I would recommend putting some grip tape on the slide, or getting a pump-action kit if that's in your budget.
It’s a great spring for an easy upgrade. I have one in a retaliator and one is in a spamf. I have one more that I’m gonna use for a super spamf too.