The rink I'm at doesn't have a pro shop or sharpener. The woman who runs the adult league purchased one (mainly for her teenage son), and she brings it to the rink and asks for donations if you sharpen your skates on the machine. I've used it 2 or 3 times. I have to say I'm not that impressed. I felt really awkward on my skates at first, and even after "getting used to it", it just didn't feel right. I don't know if it is the machine, the hollow I selected, or maybe she didn't put the skates in the machine correctly (I can't imagine how... it seems pretty idiot proof).
I'm going to be shipping my steel out to get profiled and sharpened by a professional. If the sharpening is as good as the reviews say, I will definitely continue to ship them out. If not, I guess I can get used to the Sparx sharpening.