I have the Havel's Fabric Cutter. I got it about a week ago from Nancy's N. I spoke to one of there team before purchase.
The fabric is held I place very well with full length sand like strip at the cutting edge. No wiggle which was one of my problems, I have broken both of my wrist in the past few yrs.
I just went in and tried mine with 8 layers and was just shy a little bit on last layer, but I can't push down very hard myself any more slips like butter through 4 layers and probably 6 but I did not try.
My one problem with it is only instruction are written on outside of box ,30" long, it is not difficult but these include the blade changing bit and I want to keep that.
Then at first I was not getting clean cuts all the way through! I was a bit upset, I put my thinking cap on and finally figured out that the table I was using ( a fold up craft type table) was not level, the edges were just slightly higher than the middle! It worked fine for the long flexible rulers that I had always used, but the metal one was not flexing of course ,so the blade was not touching the middle of the fabric, if that makes any sense. I turned it length wise of the table and away from the edge and it works beautifully. I would by another one if I had to for some reason.
Sorry about the book length..