I'm not sure about power but they appear to be high voltage/low current motors, where I think that most people use low voltage/high current (where high and low are relative!). Like a lot of people, I bought mine from Zapp (I think that they were
these) and apart from the voltage/current ratings, the other thing that leaps out is that the eBay ones have less than half the holding torque, and I would guess that this would also apply to torque available while rotating as well.
Not sure what stepper drivers you are using but I have Pololu boards, and based on the online suggestions (try googling something like Pololu current limit setting) I just tweaked mine to correspond to a nominal 1A limit. But that would be way over the top for the eBay motors which are rated at a lot less.
