This is a 1970's King trombonium owned by trombone soloist Miles Anderson.
Says Miles:
This is a King Musical Instruments made in Eastlake, Ohio Trombonium, serial #472689, which would seem to be from the early 1970s.
It is in very good condition, that is, no dents with valves and slides all in good working order. The instrument was recently given an acid bath. so history's crud and barnacles are gone. The lacquer is original and has the expected wear and scratches.
Added and not original are Amado water keys on the first and third valve slides. This horn can hold water like a camel, so this compromise of originality does save one from constant slide pulling.
The trombonium was promoted as an upright valve trombone, but it does not sound like a trombone—more like an English bore baritone. It is a more conical than cylindrical sound. It has a .500 bore and an 8" bell. It plays well, and its light weight makes it easy to hold—lighter than a baritone, and especially a euphonium. Lipping down the 2/3 and 1/2/3 valve combinations isn't very difficult.
The mouthpiece that came with it is a no-name in need of plating, and not worth the expense. So, I cannot say that it comes with a mouthpiece, although you are welcome to this whatever-it-is.
The case is original, and in reasonably good condition given its age. It protects the instrument, and the latches work. It does have a rather musty breath, but not overwhelming. The instrument probably went through many years of not being used.
Here is a link to some trombonium history: https://www.hnwhite.com/Trombonium%20Page.htm