Yeah, I'm on the fence about what to do. I also like that it is small enough to bring on trips. I don't like that I'm then beholden unto them for supplies. They make portable versions of regular machines but they cost twice as much as the Sparx unit.
I've only heard good things about the Sparx, but I've never used one. I would be partial to the flexibility and the customer service of established skate sharpener companies like Blademaster, but I understand that may not be a need for you.
If you're only sharpening your own skates and maybe your kid's skates every few weeks then the Sparx is probably fine for you. I've heard that they struggle with goalie skates over size 10, so keep that in mind if that's something you think you might encounter.