You should make your own mind up, but I would suggest that you talk to Mike Green at FAST at Thruxton as well as any other options. If possible, I would suggest that the instructor course is best done with another student. You can share experiences and practice on each other. It is, or should be, an intense course as well as very enjoyable.
Incidentally, the course normally gives you a resticted instructor ticket - you have to jump through various experience "hoops" before you get the equivalent of a QHI.