I've been using that for 2 months now. I would say I'm having good success. It does require that you practice, practice, practice. I have a very busy schedule so I generally only get 1 session 15-30 minutes a day.
At 2 months in I have days when the voice sounds pretty good and other days that I just can't get the pitch up and by the end of the day it always drops off. If I could get in 3-4 practice sessions a day I think that would speed thing up.
I do always have to concentrate on what I'm doing but it is getting to feel more natural.
There are 2 other girls in the support group that I go to that have used this program. There voices are very passable. They both took 10-11 months to get there.
I like the program, I would recommend it.