I saw them used/demo'd years ago on Alex Anderson's show, Simply Quilts and then had a chance to try it one a local quilt shop...
uh.... wasn't impressed, tho' we (our 15 guild members) only got to try it a few minutes each... and on a smaller size quilt than I was used to (most of mine are 60"x80" ). Like anything, I'm sure "practice makes perfect" (or close enough!).
Good luck.