The lab type cutters are as accurate as the positioning. If care is taken in that part, they do fine, but so do scissors.
I like to use a cheap Fiskars plastic paper trimmer on a light box. It's overkill but it works nicely, and even tricky situations like too-close negative spacing are easy to deal with.
Geez, I can't believe this is even a problem. Enough light and a good, sharp pair of scissors.
This is another "I can't load steel/plastic reels" thing. Nobody can the first time. Just takes some patience and a little practice.
One of the reasons I like the cutter I recommended is that only one of my two hands is capable of either accurately holding film still or cutting film with scissors
A "guillotine" type cutter solves that problem - my weaker hand is quite capable of handling the blade. A rotary cutter will also work.
The "Dr. T" film cutter adds the translucent base, guides that hold the film straight and distance markers, so it works even better than a plain "guillotine" type cutter, especially with slide film.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2