I've related several times on how I ran a lot of it through a Glock 21 in both a ”shoot to failure” (no cleaning) and to see if there was any adverse wear.
After many thousands of rounds, I couldn’t see any additional wear and tear on it.
However, Lucky Gunner did a test with identical AR's, and there was obvious barrel wear and breakages seen with the steel, but not the brass...but the money saved (it was a 10k round test) would have bought another entire AR...let alone just another barrel and a few extractors.
I have some steel in my “deep storage”—that is, when there are no more options left, I’ll run it; and, I did like running steel when I used to take super high round count classes (think 1-2k rounds over the course of a weekend class) where I wouldn’t get the brass back, either.
I truly think it's one of those things where the issues get pretty overblown...but there are drawbacks to it that need to be acknowledged.