I'll let others answer regarding the elbow and bucket style feeders - I've not used them in the past.
As to over-eating? CornishX are the only "breed" of chicken famed for eating themselves into oblivion. For the brief period when I used 4" PVC "J" style feeders (I still keep them around for extended absences, but have some complaints with them) my CX would spend the whole day right next to them, except for brief walks to get water. The rest of the flock would eat some, leave, forage in my acres, wander back, eat some more, repeat, repeat, repeat.
Ad libitum/free feeding is, in fact, a very popular management method for many backyard keepers - as long as you have good quantity feed, and don't have fast growth broilers like the CX - I would not anticipate problems.