The Planet Waves Grip Master is a tool designed to keep your fingers, hand, and wrist in shape.  I got this because I was having some tendentious in my arm from playing guitar and wanted something that I could stretch out my arm with.  While it has been almost two years since I had the tendentious and needed this, I still have this around and occasionally will grip it to keep my hands warmed up.  I'm not sure that this is necessary or will cure any sort of aches or anything like that, but it is definitely good for stretching your hand and fingers out easily without having to be playing.  It is a good work out for your hand at the very least.  I can't say that I would recommend this to everyone, as probably not everyone would need something like this, but for those of us who play an awful lot it might be good to have around to keep warm.  I don't know how Planet Waves' version of this would compare to another brands as I haven't used any other ones, but it does make me feel good knowing that this is manufactured by a company who is the musical instruments business and is catered toward guitar players.  The price of the Planet Waves Grip Master is right around where you would expect, and isn't expensive in the least.  Like I said earlier, I can't say that this is a tool I would necessarily recommend to anyone, but if you feel like you might want something like this, I'd definitely encourage you to check out the Grip Master as it has helped me in the past for sure.  I don't know if there is any medical reason to use this instead of some sort of manual hand labor, but for me this makes working out my hands easy and simple.