I second this. We have had the power drive for about 6 months. I don't think it really helps you use your legs at all. Sure it gets you in the sprinter position; however, I can show my dd the pictures in the drive mechanics thread and she can get in the right position.I have one with a ton of dust on it.... Yes, it'll get you into more of a sprinters posture, but that's about it...
I do however recommend the Queen of the hill. It really forces her to drive and not simply reach outward. The biggest bonus with it is the fact its adjustable...
I Just recently bought the queen of the hill (used a coupon code..thanks Coach James) and I am very happy with it.
First night we practiced with QOTH, dd had used the power drive and looked to be in optimal position for drive but when she switched to the QOTH, she could not get the unit to double click. By the end of that practice, she started to understand what good drive was supposed to feel like and was getting the unit to double click on tension level 1 (easy spring). She figured out that the power drive still allowed her to drive more up than lateral (even though she started her drive in an okay sprinters posture). Since then the QOTH clicks are stronger and we are getting ready to increase the tension 1 level.
Here are two pictures from first practice with it. First pic is the very first time on it when she was getting no clicks.
Second pic is at the end of practice, when she started figuring out how to drive to get the machine to click.