Lozza, I had all my students give it a try and it seems one girl picked it up pretty quick.
She has a really good snap and with the spin she has, her dad gave a "Holy C**p!!" after she pitched it. It zig-zagged over the plate. Speed is alittle slower than the fast ball, but she's already using it as a new pitch. Her's has a tendency to go inside (due to her middle finger having the stronger push on the seam).
The other girls are at varying stages, some too young, others to old with too many pitches already.