Kamp it's a very inexpensive toy. I do plenty of bar work, but having recently had elbow surgery, something that let's me specifically work my grip is very useful.
Most bar work, finger tips pushups is fairly static, I want something that allows my fingers to go through a full range of motion as well as the ability to adjust the load. Both are good, I do both.
Now if you start to add bar swings to that, I'm sure you can really develop an iron grip. Right now my grip is such crap that I can only manage a hand full of good swings with out straps and gloves.