I have the SCA 21mm bar and dig it. The only problem with it is the poly bushings, which are loud and squeaky unless they are lubed frequently. As randyj noted, it can be hard to install - the 'window' between the tank and the rear subframe is really tight for a large diameter bar. I managed to get mine it there without loosening the tank.
There has been a lot of discussion regarding the SCA clunk. I had what I thought was the clunk, but it turned out to be a severely worn poly bushing that wouldn't hold the bar properly anymore. After replacing that bushing, the clunk went away. I have seen no need to attempt SCA's weld-on clunk fix.
Overall I would recommend the SCA bar. Now if I could just get some bushings with zirc fittings....
-Kurt
