Steel cased ammo is great for guns designed to use steel cases, like AKs, Mausers, SKSs, Makarovs, etc. If you don't handload "common" calibers like 9x19, its an inexpensive option that usually works fine.
The problem with some steel cased ammo, specifically Tulammo, is that because its cheap, its also inconsistent. Inconsistent ammo is generally inaccurate ammo and can cause malfunctions up to and including blowing the gun up. For example, most documented cases of FALs blowing up are because the shooter used Tulammo or another very inconsistent ammo like Chilean 7.62 NATO.
There's also the issue of bimetal jackets, which some gun clubs and almost all matches and indoor ranges prohibit. However, brass-cased ammo can also have bimetal-jacketed bullets.
There's finally the issue of having to clean out primer sealant, but not all steel cased ammo uses primer sealant and again, brass-cased ammo sometimes uses primer sealant too.