We have four: 2 x 100L and 2 x 200L.
They are Italian (which seems to be the source of a lot of good small winemaking equipment) and made from 304 stainless steel.
The variable capacity feature is enabled by a floating lid which sits and is sealed on the wine surface thus excluding any air during storage.
The floating lid has an integrated airlock and a wide rim to accommodate an inflatable bladder.
The bladder is inflated by a hand pump which has a pressure gauge to help avoid over inflation.