A finger guard
Finger guards should go along the trimmer's base. It's a safety feature that prevents your fingers from being chopped.
A Tension Spring
This prevents a guillotine paper cutter from acting like an actual guillotine. The tension spring is attached to the blade so it won't move by itself.
A Blade Latch
It holds the blade in place when you aren't using the paper guillotine. It's usually a wire that hooks over the handle. Sometimes, it's a piece of metal attached at the bottom of the handle. Now, you may ask: Why do I need this? This prevents the blade from popping up.
Watch out for the size
Consider the thickness of the paper you'll be using. Bigger ones can usually cut through a 3-inch stack of paper.
Consider whether you're going to take it to other locations; if so, make sure it's appropriate for traveling.
One tool that does both paper and mat board vs. two different cutters?
I think that's opinion based, because it will cost more to buy two separate tools, but putting that aside:
- Economically [option 2 wins]
- The sharpness of the blade shouldn't be affected by cutting a mat board (maybe over time)
I would recommend (if you're going to use it often) to buy only one that does the cutting you're looking for... it has to be a high-quality cutter (because I suppose you probably won't want to replace it every time something happens to it).