1, Yes they do work and are worth buying, IF you have them setup right. I have cams with teeths/notches, I wind it up as as tight as the chain can go with my hands, the chain should still be a bit loose still . I then get a pair of pliers, hold onto the cam and wind it up one more notch, this makes my chain nice and tight. Smooth cams are ok...but in my experience they slip. 2, Any cams with 10mm holes will work. I'm assuming your hub axle are 10mm sized. I'm using teethed trialtech ones. Cams go on the outside face of the dropouts on your 221, like in this pic. Link. Simple to put on and no need to take the wheel off. 3, If not, for some reason, which I can't think of any in your case (on your 221 pr). The alternative that I almost went with is to use the 74Kingz single speed tensioner, but you need a longer chain for it to work right. But then it would look odd on a mod.