I can’t speak about the 12m, but I recently had the 10m Razor on demo and got @ 20hrs. on the water with it.
In 10- 12knots with a bit of current going against me I was having no trouble staying upwind on a 6’3” strapless surfboard. On the high end, I’ve had the 10m and JT 132cm out on flat water in very gusty wind with the gusts hitting 33/35knots. The kite handles gusty conditions just fine but it was completely trimmed out and definately not in it’s sweet spot.
BTW, I’m 185lbs. and an IKO instructor (just to give you some idea of rider level).
Hope this helps.