I actually had to Google "Varigrip" as I had never heard of it before. Looking at it I can certainly see that it would strengthen fingers however flexibility is also a very important aspect of effectively playing bass. If you have an hour to kill commuting then certainly use the Varigrip periodically until you are comfortable with finger strength. An exersize I do occasionally is twirl a pen with my fingers forwards and backwards, sometimes I may use a large marking pen. It takes practice but helps with strength and flexibility (and costs nothing). Incidently I picked this tip up from "Guitar Player Magizine" years ago. It certainly helped me when I was on an overseas holiday for a number of weeks and was unable to play bass at all. When I finally picke up the bass after 8 weeks I was surprised at how much flexibility and strength I had managed to maintain.
All this said there is no substitute to practice, practice and yes practice.

i'm not familiar with this Varigrip too, it might help for sure but nothing beats getting the most out of your practice even if it's limited. hand coordination is something you need to develop with your instrument. good luck

-moku

Yo Jhon,
Welcome to Active Bass! We are glad that youare here!! I agree with Terry Bros Varigrip!! :^D
Black Hawk