I saw the bucket things you are talking about, and I think the design is to limit the amount of dirt that gets into the water. Which, considering how filthy their feet get, can only be a good thing. I also think that they look reasonably sturdy, so shouldn't get knocked over easily.
However, they are hugely more expensive than the plastic ones, so you would have to go through a number of plastic ones for them to be cost effective. For the 6 hens you would need more than one. My 3 hens go through about a lt, to 1.5 lt each day and as I've said before, they do what the others do. I would seriously suggest getting at least 2 stations for your hens.
Finally ACV has lots of great proven health benefits. I won't go into them all here, I would miss some. I though the same as you, did lots of research on the matter and decided that I would def be supplimenting their water with it. After all layers pellets are made to give the modern breed of egg laying chickens what they need, suppliments and all and are a far cry from what wild chickens would get.
I'm not saying you should add ACV, but you should def search and read up on it, before you limit your choice on whether you will provide it based on an expensive drinker. If you do then decide on no ACV, and the price per drinker doesn't put you off, then go for them, they seem sturdy and well designed. This, for me, will always be an issue of being overpriced though, when you compare them to the price of galv steel feeders or hoppers, the price for the drinker doesn't seem comparable.
Perhaps that's just the accountant in me!