[JThiessen]

From my experience with people that work in the machine shops, Grizzly products are priced low for a reason - but these guys are used to running machines that hold +/-.0005" over 4'.
Jet Equipment is usually considered a step up from Grizzly, and their prices reflect that.

Are you going to be machining steel? Do you need a coolant system included on the machine, or will you apply it manually?

In the end, you want repeatability, some amount of accuracy (is your slot going to be a slot, and is it positioned properly relative to whatever you wanted it to be). The ability to do this will determine if you end up using it. Also, the ability to change speeds easily. If its a cumbersome operation to change your speeds, you will end up leaving it set on whatever you last had it set for, and likely use your dremel to cut that new part.

Like Nitrostarter said, your vices and cutters will make or break you!