My club has had the original chopper, and I was never impressed with it for real precision work. It works great doing thin, quick things repeatedly. For example, say you were cutting strip wood into identical lenth planks for a loading dock. The original Chopper is ideal for that. It's a lot faster than cutting it by hand...and more precise. But the handle can get loose to twist or even out of square, so I tended to cut items a little long and then sand/file them to fit for true precision work.
When I purchased my own Chopper, I bought the Chopper II. The rigidity of the handle is much improved, increasing speed and accuracy. The self healing pad is nice, too. About the only issue I've had is cutting long flexible stock because the cutting surface is pretty tall compared to the old Chopper's masonite base. I just stacked up some boxes or something (not a big deal).
It is true that the cut is not 100% straight up and down on thick stock. The blade is not bending. Instead, it's the fact that a razor blade is sharpened on both sides. It's a V-shaped blade, IOW. Therefore, it makes a V-shaped cut in both the piece you're cutting and the piece you're cutting off.
The solution would be to have blade that was only ground on one side. Then it would cut square. Think of our track cutters. If you cut rail with a regular wire cutter (with twin V-type blades), you get two cut edges that are pretty rough and unusable. But if you use the Xuron rail cutter with their flat side, the rail will come out pretty clean on the flat side. Same thing for the Chopper.
Unfortunately, I don't know of any such razor blades.
