I like to use rotary hacksaws in my angle grinder for al kind of cutting. Roofing/timber/aluminum.
These blades are not cheap, when one of these dual saws was on special pretty much for the price of a blade for the angle grinder, I thought I'd give it a go.

In my opinion the concept is good, saver to use then angle grinder, don't worry about having to cut trough a nail, etc.

So far I have only seen them in cheap quality powertools and that is the major downfall of them. As with any cheap powertool, it ends up being a waste of money I find.

I will go back to hacksaw blade in a quality angle grinder, I even think it's saver in long run.