It is great if your daughter is very school dedicated, in terms of home work projects, etc and doesn't have a lot of extra "work out" time. It is supposed to increase speed but also strengthen rotator cuff and balance the muscle structure on the opposite side of their pitching arm. I would say that yes it is a great device for all of the above. We have a home gym with it in there and I like her to alternate seperate shoulder exercises with the windmill so I incorporate it into her routine. Last year she wasn't doing a lot of weights as she is a naturally built powerhouse so she worked the windmill a lot. This year she is doing more weights as her speed isn't where it should be for her age, 16 on Monday, so we are still using it. I guess, because it is expensive, if she is young and not doing a lot of upper body work then by all means it is well worth the money!!!! I know that at my daughters age a lot of the kids are no longer using it as they think that there speed is where it should be. I can honestly say that by observation of my daughters freshman year, the older and "more experienced" pitchers were no faster then my daughter and she never got a chance to pitch last year. I do own a radar gun as well.
Sorry for the rattling, I hope that this answers your question.