I have never used them personally, but I have a friend who bought one a few months ago. She got the one that curves and has bumps on it. She says she loves it and has since gone back and purchased another one with ridges on it instead of the bumps. I have not asked her how she likes this one.
They are quiet expensive. I think she paid over $100 for each of them.
I plan to get one when I save up my pennies....
