Full disclosure, I've no experience with this particular model. That said, I've also heard form several unrelated sources that many of the plastic components (gears and such) needed to be replaced with metal substitutes after approx. 8 to 12 months (of moderate to heavy use). Have also heard complaints about vibration, accuracy, and precision that stem from similar causes; the size will almost certainly, at some point, become a limiting factor. The general consensus seems to be that while most enjoy these machines (Central Machinery, HF, Grizzly - all clones of one another - probably made in the same factory), upgrading is inevitable (for those that stick with it).
If you know this is something you're going to enjoy (most moped people will; did you like Lego's as a kid?) then shoot for something between 7" and 10" (and get an older model - they are better machines). Plus, by the time you buy tooling posts, tools, bits, centers, chucks, etc. you're going to be about $1000 deep anyway.
I guess it really depends what you want to do. If you're looking to turn pens, art-type pieces, or make bolts, this will probably be awesome; cutting moped stuff on thi will require a lot of ingenuity, mod-ing, and additional parts. If I were you, I'd shoot for THIS. Should be able to talk the seller down a hundred or two, plus you'll get a chuck, post, and tooling.