I have the 650 and love it. I've noticed that the right angle guide for the cutoff can be out of square, two screws hold it in and the bar has a little wiggle room, so that should be checked on occasion. Be careful to put the blade back up after doing a cutoff, it's easy to overlook and can give you a nasty slice when getting ready to cut the opening as well as messing up a good piece of matboard if you start cutting with both blades down.

I have mine on a desk set at right angle to the wall so I can stand at the end of the cutter and cut by drawing the blade towards me, much easier on the back than trying to push it sideways from the front.