Wrist/Forearm exercise

Has anybody else tried a thing called a Dyna-Flex?
I'm not associated with em or trying to push their product or anything but it's the first time I've used something that actually works the right muscles for a guitar player.
It's really weird, like a ball about the size of a tennis ball with a gyroscope thing inside. You get it spinning and just by rotating your wrist it speeds the thing up faster & faster until you're working your wrist like crazy trying to keep hold of it.
The thing I notice is that it makes your fingers work by trying to hold onto the ball, but mainly the forearm gets as tight as hell like you've been playing hard rock for an hour.
Like if you've ever played in a band doing hard rock and started off with a fast song without warming up first.... that tight feeling you get just above your wrist.... This ball thing works the same muscles but about twice as hard as playing the guitar.
Just thought I'd pass it along for anybody who's looking for ways to strengthen their fingers or an alternate way of exercising.

I'd rather just play guitar.

Actually I got one & was suprised at how well it worked. After using it you feel like you've been playing for 5 hours.
(just don't lose the string... despite their advertising there's no way you can start the thing up by hand)

where do you get one of these things and how much does it cost. Is it made just for guitar players or is it a general exercise thing. Sounds interesting.

in next couple months i will be puttin together a band anyones welcome singers bass players guitars drummers . i allready have a bassist guitarst and singer but if ur intreseted email me my email is ganjasaurous420@yahoo.com the type of music imk goin for is a mix of metallica and tool so if u want to hit it big someday email me

I think they're about $20 from sports type stores or just do a google search for Dynaflex.