Here these types of restaurants are already part of the culture. Sushi, pizza, barbecue, pasta, crepes, mini burgers and appetizers, asian, arab/lebanese, mexican and many more. There was even some milkshake all-you-can-eat at one point!
I eat a lot, but most people don't eat that much, I think one of the "charms" is the variety. You can eat a little of each instead of buying a single big plate, and also most of them charge for the drinks, so there's profit.
Tthe ones in my area are usually slightly more expensive than à la carte, but like I said, one of the charms is earing more variety. (But people like me and my friends do get ours money's worth, we eat a lot. Hahaha)
Never ate it. I heard people praising duck à l'orange, I've always wanted to try it.
And I'm kind conflicted towards foie gras. I know it's cruel, but it also looks good.
Some of them, like the barbecue ones, usually you serve your food at the buffet table, but most of them you have to wait for the waiter. Usually it's okay, but I had experiences when there's wasn't enough of them, or you asked for food and it took a long time. In a sfiha (lebanese food) all-you-can-eat one time I ate less than 10 of them, even though I certainly could eat like 50. We asked, asked, asked and the food never came.

We complained to the manager and at least they gave us a takeout box with some some of it (which obviously they don't do in these types of restaurants). It was less than I could've eaten if somebody bought the food, but still better than nothing.
But I also heard compliants that were like very, very, veeery dumb and obvisouly the client was at fault.