I have the set up in two shadow 2’s. I don’t think the rrk is totally necessary for someone with average to large hands. I do see how it can help with shorter fingers. I like the adjustable sear because I can set it stiff on the safety so as not to unintentionally activate it but still pass safety check.
If I were ordering parts for a new s2 I’d get new springs, ext fp, old style 85 trigger, and a Comp hammer. With the rrk the disco is pretty much fit so you won’t have to do much to it, at least I didn’t.
One thing I didn’t like was the reduced power trs. It made for a mushy trigger and reset wasn’t as tactile as I’d like.
Im sure I forgot something but others will chime in.