Let me preface this by saying that I'm not positive that the AC SS hub uses the same mechanism that their normal cassette hub does. If it does, however, I'm not impressed with the engagement system. In the normal cassette hub, the pawls don't actually contact the hub shell when coasting. This is fine in theory. However, the mechanism that re-engages the pawls when you begin pedaling is nothing more than a small wire, which engages a cam plate, which then engages the pawls. In my experience as a mechanic, this is a frail system that often fails to work correctly or just plain breaks (under a lot of force, I've seen the small wire break off). I know there are lots of folks who like the AC hubs for their light weight - however, I'll take a little more weight in exchange for solid, unquestionable engagement. DT Swiss, for example.