I have skiied both and found them to be VERY similar. I found the dynastar to be even stiffer than the Mantra, that seems to be the primary difference. I thought the Mantra floated a little better (although they are both kind of bottom feeder powder skis, you need lots of speed to keep the tips up, built more for versatility in powder-crud-hardpack than one particluar condition).
I ended up on the Mantra and I'm happy with it. Rip sticks.