Steel cases don't go down the barrel. However, steel case typically has a bullet that uses a steel jacket which is then copper plated. It's very soft steel, about the most garbage steel you can find. Still harder than copper so it will wear faster. Whether or not the wear is acceptable for the cost savings (buying more expensive ammo or a replacement barrel), is going to be a personal choice. This topic has been beaten to death way too many times.
Another option is that you could INSPECT the snake before/after using it. I guarantee that you will get your money's worth before the thing wears out. You'll get your value from it saving time and effort when you don't need a super in depth cleaning.
I have a 5.56 snake that I got second hand a couple years ago. Unknown how much it got used before hand. It's lived it's life with my soaked in clp/rbc, it's been pulled through the bores of hundreds of rifles, many times. I use it nearly every time I shoot an AR on my own time. It's had easily one thousand pulls and not showing any wear.
By the time and effort it has saved me, and the hundreds of other guys that I let use on their rifles, it was worth $20.
Again, it's not a replacement for the cleaning rod, it's a totally different tool.