i dont know much about nines but masterminds are a pretty playful ski. if you've ever ridden line invaders, they are very similar to those in relation to amount of flex. they have really nice butter zones too. Theyre not true twins either. I belive they are aimed towards more of a beginner but they can definately handel anything (LJ strenio skied on em for a bit im pretty sure)
So, if ur looking for a fun, flexible ski, i'd definately reccomend it.... but if u wanna be hittin some groomers here and there still or alot of fast switch riding, get a stiffer ski.