Just so folks don't get the idea that I'm subborn or opinionated about Rotatrims; I have four guillotine trimmers ranging from a 50+ year old 12" Premier, a 20 year old 24" Premier, a 15 year old 15" Ingento, a 3 year old Harbor Freight 12", plus a 20 year old 16" Rotatrim, and a 15 year old 30" Rotatrim. Some are easier to use for certain tasks, that's why I keep and use them all.
They all cut cleanly.
I keep them sharpened.
Especially with guillotine trimmers, use a professional sharpening service.
$30 in the hands of a pro, and you'll have a new trimmer.
Before I retired, my profession was in the technology of slitting flexible web materials (Google my name Reinhold Schable). In my consulting jobs it was a constant task to convince people that the basic requirement was to keep two properly sharpened edges in intimate contact when slitting any material. It seemed that everyone wanted to buy the latest wonder gizmo instead of learning what constitutes a truly sharp edge and how to keep the two blade edges it in their proper relationships for a clean slit.
Keep those edges sharp, and keep those blades in intimate contact
End of sermon.