These sandao hand grip ring trainers are the best and totally work and are a good size to be portable. I'm always working on my grip strength and these are nice as they came with three and I could put them in various locations. I drive about an hour each way to work and so it is nice to have them in my car to do a few reps while driving. I also keep a set of the harder ones at my desk at work. I have found that they are also a little like stress balls in that if I use it at work I tend to relax a little after using them. Overall great buy and I highly recommend.