Particular
Disassembler, occasional reassembler
Every time I try to cut it I always end up getting some jagged piece and it's practically impossible to cut it curved like the template because the film itself is so bendy and stiff. Do you NEED to cut it at a curve? What's wrong with a 90 degree angle?
As I mentioned earlier, I don't cut the film, but use a card to load my IIIc. A lot of the film I use is bulk loaded, and I mix it between an M3, M6, IIIc, and now also an OM4. In an ideal world I would have my film prepped and marked, with different leader cuts in my fridge, but in reality, I just tend to grab something on my way out the door.
I have found myself a number of times on my bike by the side of the road with my M6 and a leader that is cut straight, without a scissors. I have managed to just rip the leader roughly into the right shape, and, yes the cut is jagged. It still works fine.
On the IIIc/IIIf, I don't think the cut is that critical. A tight corner could rip, but only if you pull the film hard. Sharp edges, and cut sprocket holes could catch on something. I haven't noticed this happening. The purpose of the long cut is to bridge the length of the shutter opening, so it won't snag when you push the film down. It should not be hard to eye it. There is no penalty in cutting it too long either.
When using scissors I tend to find large ones easier to cut slow and precise, but I really should get a small pair for in my camera bag.