It's good for darkening up small dings and gouges in items that are otherwise anodized dark gray or black.
Even with padding on the pliers, I messed up a suppressor cap something fierce when it got seized up, and was able to darken the gouges so it looks decent from a distance of a foot or more.
Does it pass close inspection? No way, but it's a vast improvement.
I suppose if small aluminum parts are cleaned and prepped well, a single dunk in the solution will blacken them nicely, but the major drawback is if you try multiple applications, the blackened surface will react with the solution and it'll change colors and fizz creating inconsistent results.