I’m not saying you can’t use another type of ruler but there are benefits to use the plastic rotary cutter rulers. They tend to be thicker so there’s a less a chance you’ll accidentally go over the lip of the ruler and instead stay on track. If you do manage to go over the edge of the ruler, which I have done from time to time, the stainless steel could nick the rotary blade, which would be bad. Hope this answers your question. You can find these rotary rulers in the same section that they sell the mats and cutters.

Mine looks like it’s about an 1/8″ thick and it’s been pretty good for me. Only went over the edge a few times 😉