A friend of mine purchased these, and his grip is now amazing after using them a few times per week for a few months. Since we practice a martial art in which hand strength is valued, I'm purchasing them as well. He has the 100, 200, and 300. I can easily close the 100 over 50 times, so it's a nice warm-up. I struggle to close the 200, though, and neither of us can move the 300 appreciably, despite my buddy's ability to close the 200 about 20 times now. If you want to develop with these, don't skip the 50's!