A brake booster would aid the rigidity of the frame, but its not a must have. If your that bothered about flex then by all means get one because they do work, but the Blade should be okay without one. As for two or four bolt I'd go two bolt, simple because I had a four bolts for a period and it was pants. The only other thing I can comment on is the Tensile (as its the only thing on the list I have), they are great freewheels for the price, mine has lasted for ages and has'nt skipped once, although I know of a few going wrong and even exploding, in general they are very good. hope this helped.