I run a single dubz (wtf?) on my drive side and think it works incredibly well; light, doesn't get caught up in fingers, and has semi modular components that let you mod/customize it pretty easily (I switched my bolt out for a longer one so i could keep my wheel real slammed.)
So for me it was definetly worth the 15$, but if you do run both tensioners, that 30$ does seem a little steep.
-Kai