This rear derailleur has been pictured once in this thread on a build. One of these 5800s came to me on a bike with mixed parts. I am not as fluent in Superbe as many here, so it took me a bit to track down this one. It is listed on Disraeli Gears.
I am not using this right now as I don’t really need the chain wrap capacity. I also find it a bit clunky looking. The build quality is fantastic, and I did have it mounted on something once, and it shifted wonderfully too. Eventually I discovered that this RD was stock on some Cannondale tourers from the mid 80s. I came across it by accident and that is the only place I have seen it used.