I got one for xmas. I've been using it everday now for the past 3 weeks. I've deffinately noticed and increase in strength and distance. I used to hit a PW about 125 now i'm hitting it about 135-140. I feel the main increase comes from added strength in the wrists allowing me to hold the wrist cock longer and release the club later. I've always struggled with early release.
This added strength has got me thinking about golf fitness. I'm gonna get down the gym soon and start a fitness program
The powerball is definately worth a try. It's a bit of fun really but it'll deffo inpprove the swing.
Hope this helps
Daz