The first roll has gone through my Minolta X-570 with the cool power winder from the Denver swap meet. It's the Power Drive 1 with the upright piece that gives a larger grip and adds 2 shutter release buttons - 1 for landscape and 1 for portrait. It takes 8 AA batteries and should have enough juice for 100 rolls of film. It can be set to single shot, and slow or fast repeat. I've been wanting one for a couple of years, especially for shooting surfers on vacation.
I like it. The camera stays on target better between shots. The grip feels much more natural. The added weight makes the whole package more stable and I'm thinking it might give another stop when shooting handheld. With the extra shutter button there is no more bending the wrist around over the top when shooting portrait. On the down side, it is really noisy.
All in all, a pretty well spent $35.