Cutting extruded aluminium with a circular saw
For blade selection the higher tooth count makes for smaller chips which is a good thing as each chip cut is an impulse against the work and the tool, and smaller impulses are better.
Circular saw blades tend to grab in aluminium I wouldn't risk it hand-held:
when using a drop saw a slow feed rate is essential else you stall the blade or distort the work. A hand-held circular saw is likely to be uncontrollable.
If you're persistent a hacksaw will work.