i would say that the 90 mph club is a wise investment, especially the Extreme pitching DVDs. Its for the whole body not just the arm. The goal of it is for you to be able to work out harder, longer, more often, and smarter with anything or nothing. You learn a lot of creative workouts such as stuff on stairs, hills, playground, walls, sand, tables, trees to name a few. It also strikes home a point that really makes sense after you hear it.... NUTRITION. The spend a fair bit of time on that. It's mainly workouts, a brief section on mechanics about 20 minutes or so: mainly find what works for you. Overall, the main goal is to improve body control, balance, and athletic ability.
I would say if your looking for way increase your pitching control, velocity, and movement this is definetly a wise investment.
I have done the workouts consistently for about 3-4 weeks and have gained about 3-4 mph. BUT the big thing is my control, I recently went to a camp down in florida and I could absolutely paint with my 2 seamer and circle change which I had never been able to do.