+1000 on getting extra springs. I ended up having to reassemble the sear cage on my PCR recently when I was installing an "Old Style Trigger" and promptly lost the firing pin block lifter spring. My next step was to go to the CGW site and order 3 of each of the three springs that are in that sear cage. Of course, when I put it back together, I only needed the one I had lost, but having the extras was cheap insurance if you ask me.
All three of my CGW guns have the Pro Kit, installed at CGW, and they are great.