Steel plates are generally safe targets if you use them right. They are safe up close with lead bullets, because the lead "splashes" on the target instead of bouncing off it. While you may still get hit with backsplatter (I have, many times), it will generally be just a fragment of the original bullet and won't do much damage. The worst I ever took was a fragment of a 250 gr .45 bullet that hit my just below my protective glasses and hit hard enough to cut my cheek. It just bled a little, though -- not even enough for a Band-Aid.
Angling the targets to direct splatter and ricochets down is good practice, but doesn't guaranty anything. Once the target has been shot even once, it starts to dimple. Before long, it's covered with pock marks and divots. Bullets and fragments come off in funny and unpredictable ways when they hit those. Also, many steel targets have mounting hardware (bolts, etc.) that protrude through the front of the target, and hitting those will cause odd ricochets.
I don't think I'd risk shooting steel with a rifle at anything less than 100 yards, and with a big mama like a .50BMG at anything less than 300 yards, especially after seeing that video. As my daddy always said, Only a fool learns from his mistakes -- a wise man learns from others' mistakes.