I got the Durston 12" Heavy Duty Bench Guillotine Shear from Rio and
I love it.
It’ll cut non ferrous metal as thick as 4mm (8 gauge -B&S gauge),
and mild steel 2.5 mm thick (12 gauge).
It has an adjustable stop ruler. It leaves a nice clean edge, and
you can flip the blade if it gets dull (it has a total of 4 useable
cutting edges). My shear has seen some serious use and the blade is
still in great shape. I was tempted to get a smaller 6" shear, but,
I am soooooo glad I got the bigger one.