Great for one thing. Being short and stocky this dug into my chest. I never found a great position and probably mostly user error. I passed on buying for that and the space it takes when not in use.
It kind of felt like using powerblocks without the convenience of a powerblock. In all practical application I would rather use a dedicated dumbbell or kettlebell instead of this design.
I'm a fixed dumbbell snob but get to use these pretty regularly at a friends gym and they are awesome. The knurling is just right and easy to switch out weights. Feel as good as an adjustable dumbbell can.