I've used miter saw (ally is soft so a fine tooth wood saw works), pipe cutter and just a hack saw free hand in a pinch. Its not really that critical unless you're blind and cut a 45 on there or something.
Thing about pipe cutters is that they can make quite a rise at the cut, esp if the material is thick. This is because they cut by displacing material to the side rather than removing it like a saw, so on thick ally bars you'll probably have to file it back down on the outside to make it the same OD to get grips etc on.
Oh and if you take it easy, recon a skill saw would work too, make a vid if you try it though.
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