they are more ornamental than anything else. I have a clay one. You cannot really have a large fire in it, lest you crack it. It you get a metal one, you need to be sure that no one touches or falls against it when hot, or else thatever part of the body that touches it, is cooked!
on the plus side, I can burn garden waste and pretend that I am heating up the BBQ if any nosey neighbour comes to complain about the smoke!
you can BBQ on them, but the grill area is quite small.
I would be very reluctant to burn coal as it would get too hot and perhaps crack the base or sides. It is really onely useful for small timber. It is not a patio heater in ireland. It may be in Mexico, but not Ireland