Barrel block is the most popular Vic, I have both the v block and the delrin sleeve set up for mine , it came with the v block mounted to it and shot pretty good so I never tried the other so can't comment on it are you looking at buying one or making one?
I liked the first one so much I bought another!
nothing shows a good or bad component like a rail.I test seating depths , powders ,bullets ,primers even brass lots in the rail , if they are going to have issues the rail will inherently show it quickly
when I first looked at buying one I thought it would just be something I needed to shoot the nationals ,never would have guessed how much fun they are to shoot,