They're great (although that seems pricey, I got mine for about £1.5 each. I got a bunch and they're so cheap I didn't even mind when I let the magic smoke out of one).

They will only provide 750mA max, though (and ideally you want some cooling to run at that level for a long period).

Stepper motors:

More current = more torque.
More voltage = more RPMs.

The motors I ordered are rated for 4.5/5 amps, but when I ran them on my 750mA drivers they were still pretty strong. Don't think that'd hold up to machining, though, as I could stall them with a pair of pliers pretty easily.