The examiner who took most of my check rides hated it, when we were hovering to low, even in R22's. He always argued that, by trying to be prepared for the unlikely event of an engine failure in the hover, we were taking far greater risks of having a dynamic roll over or a tail strike. After several thousand hours of bush flying now, I must say, I totally agree with him. You can get pretty good at hover auto's, even from a lot higher than 3ft, if you are expecting it, but then again are you always expecting it? If that engine abruptly quits on you in a hover, you will turn at least 90° before you even know what happened. Hopefully we'll all be quick enough and make a safe hover auto, if that ever happens, but it's almost impossible to recover a dynamic roll over. The video of this tragic event is a prime example for that.
I rather hover a bit higher and stay away from air shows as an active participant.