Many years ago I purchased a cheap Matin guillotine type film cutter, I must have run more than 500 films through it without any problems. I recently saw the Film Killer for sale at 25% discount, so I went for it. It's made by Optik Oldschool GMBH in Germany, and there are several dealers who supply it. I find the guillotine cutters to be the best solution, especially for films that come out of some old cameras that has less than one mm spacing between frames. Both my old Matin and the Film Killer has markings for exact positioning of the film so that you do not risk cutting into adjacent frames. I use a LED panel beneath the cutter, makes it much easier to see what you are doing.
Here is a picture of the Film Killer:
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