Have bought several of their trainers and they rule for building up strength at least.  Have no problems throwing a 16lb ball now and actually have problems throwing my old 14lb spare ball due to being so light throws off my aim.  I would recommend getting the power trainer to build up swing muscles and release trainer to build up forearm, wrist, fingers and tendons.  I also got the swing trainer and its good but not really necessary if get the power trainer (a good step down in weight at end of workout and good for other family members if not as strong plus it is a bit better for diagnosing if using back muscles to pull too much)).  Also got the axis trainer and neat to throw but of limited usefulness.  Finally I also got the feel trainer and like the axis trainer of limited usefulness for me.  They might be more useful later though when need to work on isolating or working on something with my release.  Made me stronger but hard to say if they improved my game or practicing a lot over the summer did but probably some of both.