I've heard of them, but mostly just from seeing them online, either on that link, or like AmmunitionToGo. Some I have seen because the gundog sites carry them. But the Rio and Sellier and Bellot, I have heard or seen other folks using those. The S&B, I think its the novelty of the almost clear hull and being able to see the shot that folks first purchase them.
Good prices both there and ATG, about the same. I have a friend who will buy from PalmettoStateArmory quite often. I have never purchased from them cuz they dont have much in the way of 12 ga. but he buys 556 ammo enmasse and gets some really decent prices.
Reloading being another topic, I know another guy who is reloading the equivilant of Hornady match for like .17 cents a round.