Lot of misinformation out there.
Steel cased ammo is generally inaccurate, dirty, smelly, usually underpowered and cheap. Other than that it's fine.
Some AR's don't like it, some do.
I've fired many thousands of steel cased, way more brass cased, depending on the gun and the task at hand.
I have friends that have shot many times the number of steel cased ammo than I have, with nary a problem.
The only issue I've ever seen is if you shoot steel cased ammo, and plan on shooting brass cased ammo after it, make sure you clean the chamber really well. Because the steel case does not seal the chamber very well, (just like .45 Colt ) carbon and traces of the coating (lacquer is worse than poly) build up in the chamber. When you then shoot brass, the brass will stick in the chamber and extractor will pull the rim off.
The steel that quality extractors are made of, is way, way harder than any steel case, they are pretty soft. Unless you are shooting 1K rounds a month, you are unlikely ever to wear one out. Same goes for the barrel, the copper washed steel jackets do impart more wear on the barrel. The cost savings using the steel case ammo will make up having to buy a barrel after 10K rounds, versus 20K rounds.
If you are just shooting dirt, or steel targets, and don't need sub MOA performance, try a couple boxes and see if it works in your rifle.