said by bbear2:Thanks. So with the 110V, it might take more current and hence heat up the motors, etc?
Depends on the type of motors used, how they are powered (direct from AC or from a DC power supply?), and the type of mechanism they are driving.
What can happen with motors run at too low of a voltage is that the motors may not have sufficient torque to come up to operating speed. Motors that are not at operating speed draw more current. Worst case scenario is if the motor isn't able to spin at all, it would draw much more current.
Induction type motors are much more susceptible to this than universal and DC motors.
Anyways, overheating doesn't happen instantly, and it should be pretty obvious if the motor isn't running at the proper speed due to half the voltage. I'd say the risk of plugging it in and giving it a quick test run should be relatively low, but chances are high that if it is only rated at 220V on the device, it probably isn't designed to run at 120V and will probably not function properly or at all.
How is the massaging device powered anyways? Does it connect directly to mains or does it have an external power brick?
said by bbear2:Any concerns about the 50/60Hz difference?
If it uses induction motors they would run a touch faster. If the electronics use the AC frequency as a timing source (for a clock, timer, etc) it obviously is going to be inaccurate (too fast). But other than that not a huge concern.
said by bbear2:And then what about a stepup stepdown transformer, if he uses that will all be fine?
As long as the transformer is rated to handle the load of the device, yes, there is no problem with using a step-up transformer.