I recently purchases a Busch Polyfocus 4x5" zoom finder by Tewe, and yesterday I used it in the field for the first time. It was probably made in the early 1950s.
It came with a nice leather case.
The finder weighs 363 grams (12.8 oz.) and is 108 mm (4.25") long.
It zooms from a range of 88mm (3.5") to 381mm (15").
It has a base for mounting in a flash shoe, and it includes a tilt adjustment for parallax. The base makes for a very tight fit in a flash shoe. If I were going to use it mounted on my camera, a Toyo AX, I'd sand the base to make it slightly less wide.
Overall, the finder works well. It zooms smoothly, and while the viewing rectangle does get a little bit smaller when zoomed to the longer settings, it's still quite large. The optics are uncoated, and so there a fair amount of flare. Outside this proved to be no problem, but I also did some photography inside an old barn, with sunlight streaming through the slats. In that situation the flare made it hard to see through the finder. Thus, if you photograph a lot of high-contrast backlit scenes, you'd probably want to find a multicoated finder.
In any event I enjoy using the finder. It speeds up scene selection, camera placement and lens selection.