I've not used alum,the aftershaves are all I need. Some have witch hazel others don't. I can tell if I've " over shaved " by the burn. Doesn't happen very often. My wife just uses soap or body wash to shave with and has always been happy with the results no other treatments except maybe a moisturizer. In Florida dry skin is seldom an issue.
Unless I get a cut, I do not use alum on my legs. I tried it & did not find it helpful. But I do use it as an underarm deodorant. For that purpose, I find it very effective. For my legs, I usually finish with a lotion stick, after toweling off.