For me, the biggest difference is that I hated the Waki's pommel (it's like two horns pointed at your belly). I posted a question about having them removed at the shop, but never got a reply and couldn't make myself pay full price for a blade that I felt the need to take a grinder to right off the bat.

There was also the BladeForums post about Dan shooting the Scizzy with a .50 BMG round -- it was only a graze, but no damage, which is fairly impressive:
Dan Throws Down With The 50BMG And The New Scrap Yard Scrapizashi!!!!!!

Here's a link to a spec comparison posted by md02geist:
Waki vs Scrap Spec Comparison