Currently the Matin 35/120 cutter is the only option. I have one and this is my 2nd one. It is fine for 35mm but for 120 it doesn't cut totally straight and the last corner always gets stuck. thought mine was just a dud but I returned for a 2nd one and it is the same... it would be a good design if it was made better and worked.
I would like to cut straight 120 slides perfectly easily. ebay isn't turning up much just some expensive hasselblad cutter that looks like a pair of scorers with a guide.
It appears to be.
And the last corner does exactly what you describe if you don't apply a slight amount of side pressure.
I wonder if they can be sharpened?