Tried a power roller, and discovered a couple things about them.
1. The time you might save using one of them, will likely be used up in the time it takes to thoroughly clean one after you're done using it.
2. The power paint stick that I bought got HEAVY, fast! Doesn't help that the ceilings in my house, instead of being the standard 8', are about 4" higher. Doesn't sound like much, but if you're not used to holding something at the height it takes to roll a ceiling, your shoulders are going to kill you, quick!
I ended up ditching the power roller for a regular old roller and pan, and actually like the results better.....but that's me.