Hi Nena,
I don't know if this is going to be helpful or not, but I have the previous regular size Viking Mega Quilter and it is working great for me. I had a little trouble getting the upper thread tension adjusted, and it looks like the 18x8 mega quilter has the same mechanism.
It wasn't the machine, it was just me. Once I adjusted the threading, it has worked great . . . for what it is worth.
I agree with the other post-er, try to get your hands on the machine to try it out.