Paper trimmer

Yeah I think you're right I will not use it with plastic sheet. 

It probably wouldn't do a very good job on anything much thicker than lamination sheets.  Rick.

I wouldn't use it for cutting styrene sheets, for the reasons Bgrigg noted, and also, it's so much easier to use an X-Acto knife and a straight edge.

Then yours is different from mine. I wonder how it sharpens the blade? I wonder if it's just a means of honing the blade, like a knife steel?

Give it a try, you might find it works well. The one I have is used by my wife who does paper art. She would trim off a certain part of me if she found me cutting plastic on it!

Bgrigg

Styrene is also much harder than paper and quickly causes the blade to dull. 

It's the reason why I asked this. But  the instructions say "Self-sharpening blade".

I have a similar cutter, and have experience cutting both paper and styrene on "professional" grade cutters designed for the printing industry.

The lever design causes thicker materials to wander as the blade comes down, and I would be concerned that you wouldn't get straight cuts with styrene. Industrial cutters use a guillotine slicing action and a positive stop that it cuts toward. They also use hydraulic clamps that insures there are no unintended movement of the material.

Styrene is also much harder than paper and quickly causes the blade to dull. At the printing company I work for, we always swap out the blade after cutting styrene and send them out for resharpening. If that blade is like mine, it is a thin blade that is plastic riveted to the handle and I wouldn't risk damage to it. I find a straight edge, a sharp utility knife and careful cutting from both sides is the best method of trimming styrene.