I have seen home made versions of those set higher off the ground, made out of wood that looked much safer. With my round ring, it is a possibility that a horse could put a hoof through one of those rounded bars - that would be scary. Hasn't happened yet - not to say that it can't.
Of course panel fencing, cross ties, hitcing posts, and a lot of other equipment made for horses can be hazardous to a horse in the right situation.
We can make things as safe as we can, but sometimes horses are still hazards to themselves