I bought an electric shear like this
If you do alot of sheetmetal work it is worth having one of these.
I can cut right to a scribed line and it makes minimal or no distortion, although I prefer to cut it a little fat then trim it with some hand shears.
It does cut 1/4 wide strip out of your metal, so you can't really use it to trim stuff under 3/8" oversize.
I had an air version of those shears and didn't like them as much. (they were cheap ones though).
I also have an air nibbler , but it is not very accurate in a straight line.