I think it depends on the individual, what moves you already have down, and the type of powermoves you decide to tackle simultaneously...
For example, learning flares and windmills at the same time probably wouldn't be as effective as learning flares AFTER windmills because the leg action from the windmills is fundamental to mastering flares. For some people they would feel overwhelmed by focusing on more than one move at a time, where as someone else would find it boring to work on only one.
I prefer to work on several powermoves at a time, but I set a priority for each. Right now, my big focus is flares so I spend more time on those. To change things up I work on aerials, crickets, and swipes.
I think the benefit of practicing two very different types of moves at the same time, improves your overall fitness and coordination that you wouldn't get from focusing on one at a time... But that's just me.
