Steel case is perfectly safe to fire, just wears your barrel and extractor out about 2 or 3 percent more quickly than brass, and as previously stated, it's dirtier.
In normal times there are those that have calculated that it is actually more cost efficient to run steel case than brass because even if you had to replace a barrel a couple of thousand rounds earlier than with brass, the cost of a barrel is still cheaper than the price of brass ammo you would've shot for a longer barrel life...right now that's especially true, although steel case is not the dirt cheap stuff it should be.