Was looking at the powered shingle cutters - basically a pneumatic auto body saw with a big hook blade - and saw a video of a guy using an multi tool.
Using any blade that has a radially aligned side, it will cut like butter. AND it leaves a perfectly smooth edge - not a ragged one. NOTE: The cutting action you want is the side of the blade pounding it’s way through the edge of the shingle - NOT the slicing action like when sawing through wood.
There are some hook blades that would work nicely too, I am sure, however, I used a crappy scraper blade that came in a WalMart pack. The blade can easily be “resharpened” because it is not the sharpness of the edge, but it’s profile.
I’m working on a small 7 square hip roof with 4 dormers that is all cutting. Seriously, putting 2 full shingles in a course is a joy to behold. There are only about 6 courses that run from hip to hip uninterupted. 160 pieces of step flashing, over 100 ft of ridge or hip. LOTS of cutting. Now it’s FUN!
… I take that back, not fun, but maybe a little entertaining… Doing job solo and WANT IT DONE.