My surface grinder is a 6x12, and there are many times I wish I had a 6x18. What I can tell you is... from research and experience, I've learned that ALL the 6x12 import surface grinders sold in the U.S. are made on the same factory floor (actually a ship/barge).... and are shipped to the U.S. in containers of 36 machines..... they are off loaded at the port, then based on each companies order, a given number are uncrated, painted, and the company stickers applied....then recrated and sent to the companies. It you look at pics of various brand 6x12 surface grinders.... there's a striking similarity. What I find funny is that something like a Harbor Freight model sells for about $1k..... while the Grizzly sells for $2k.....and the ONLY difference is the color of paint, and the stickers on the machines.
Pay VERY close attention to the mag chuck they include with any surface grinder..... generally they provide a "standard" pole mag chuck..... that means the magnets are spaced at 1/4" intervals. This works for larger heavy pieces of steel, but if you intend to surface grinder things such as smaller blades or folder parts, a standard pole chuck just doesn't work. Years ago I had to replace the finish shop door because the standard pole chuck I was using didn't "hold" ...and the part I was working on launched THROUGH the shop door (lucky it wasn't me).
A fine pole chuck has magnet spacing of 1/8" or less. They are usually far more expensive then standard pole chucks, but you have to ask yourself if it's worth not having steel parts wrecked, and/or flying around the shop.
From what I can see on Grizzly's site, they only offer standard pole chucks..... for knifemaking, I think a standard pole chuck is simply a waste of money.
Personally, I took my time and kept an eye on ebay..... I picked up a Suburban brand fine pole chuck (6x12) for $250. What I found it that the best surface grinder in the world isn't worth a hoot unless you have a "good", fine pole chuck..... at least for what I most do with one.