I have just aquired this little viewfinder for mt Sigma DP1 that comes with a fixed 16.6mm (= 28mm in full frame terms). I have also looked at a variety of viewfinders owned by a rangefinder fanatic who owns some very expensive Leica finders.
The Kinegon tele-wide was also marketed under the Yashica and Petri brands but as far as I can gather were all identical. It come with a wide and tele frame integral to the view.
I have compared the Kinegon tele-wide to the Braun 38mm to tele and much to the more expensive Sun and Leica finders. The issue was to match a finder to a 28mm (full frame sensor) equivalent lens - that accurately encompasses the field of view, lacks distortion, is bright and has a good dioptre correction to magnify up to an expansive image.
The verdict - the Braun is good but has barreling to a near fisheye look and encompases about 28mm. (Note that the Braun had the window removed from the front to get the full use of the glass. With the window inserted the Braun gives a 38mm full frame field or 51 degrees horizontal). The Sun viewfinder was allegedly a 28mm lens but framed to about 35mm only. It was bright and sharp.
The Kinegon (read yashica) telewide has a total frame of 28mm. The outer marked 'wide' frame corresponds to about 35-40mm and the 'tele' frame in the middle to about 70mm.
The view is bright and sharp and BIG with no discernable barrel distortion. It is thus a first class choice for a finder and is comparable to the Leica finder in terms of its image quality. It is a fantastic choice for those wishing to match a 28mm lens of a FF camera (or 65 degrees horizontal angle of view for the appropriate sensor / focal length combo).
Finally this whole viewfinder issue makes you think hard about angles of view. Finders of course (unless they zoom) have a fixed angle of view. The Kinegon is 65 degrees. That equals a 28mm lens on a full frame sensor and 17mm on an APS-C sized sensor. This can be very confusing and has to be carefully thought throght before purchasing blindly say on Ebay.
Angle of view is the best guide and ideally the vendor should be able to make that information available. In terms of calculating that for your camera + lens, Max Lyons has an excellent on line calculator at this site::
Attached are images of the Kinegon (left) and the Braun (right) .