If you're talking about this [Link: smarthome.com] Add-a-Motor it's what I use for masking control.

I use two (one for each panel).
Pro's:
Cheap $62 at Worthington
Decent quality

Cons:
Noisy
Gear ratio a bit high, so you might have to devise something to gear it down if your travel distance is going to be small. I use a block and tackle type pulley system.
Must remove power to change direction (perfect for an X-10 application)
Only one stop setting (it is adjustable though)

Long story short. It works fine with some creative engineering!! I'm happy with my system.