'asterGrip & VariGrip

[Plendakor]

So while cleaning my basement and making a nice little toolbox for my guitar corner, I found those 2. Can't say I've really used them before (a few times, few minutes).

So I'm looking for some testimonies here on the benefits or cons.

 

[savage_messiah]

As far as I'm aware there are no cons. I have one, don't use it much anymore. Definitely increased grip strength, but I never really noticed a change in my playing. Perhaps endurance, can't say for sure though. Probably down to me not practicing or playing guitar enough though. These links may help:
http://www.livestrong.com/article/171960-gripmaster-hand-exercise/
http://www.thebetterbackstore.net/Gripmaster.html