I really like these little cubes but I'll answer a few questions you might have. The keychain one is only really good for decoration. It doesn't move particularly well and you can easily pop out a corner of you're not careful. The 3.5 mm is perfect to keep in your pocket, it's not too small to practice on when your sitting around. I take it with me everywhere. The 4.5 will fit in your pocket but not that well. Both the 3.5 and the 4.5 both turn a lot better than you'd think. They have decent corner cutting and don't bind up too much. I'm very happy with my purchase.