i have one - didn't know what i was getting into when the shop ordered it for me - but it's been just fine. I'd say I have upwards of 800-1,000 miles on it by now - it's been about 2 years of commuting.
I did buy the tool from amazon for removal though - really annoyed about it. And as mentioned above there were some issues getting the wrnech over the nuts and onto the freewheel.

won't be buying another ACS when this one dies.