Simon, they are quite decent lenses. The 'newer' 200/4, as opposed to the 200/4.5 is better, and in the 280/4.8 lenses the later ones are truly excellent. The later 280/4.8 lenses can be recognized by having an M bayonet at the rear and being equipped with an integral tripod socket. They are fatter toward the rear than the ltm versions, focus closer and have a Series 8 filter arrangement whereas the earlier ones use 58mm filters. They are correspondingly rarer and more expensive.
If KEH shows a tripod mount on a 200, either f/4.5 or f/4 it means that they are showing it with the OUBIO adapter attached. The OUBIO makes up the difference in flange to film plane distance between the Visoflex I which accepted only ltm lenses and the later Visoflex II, IIa and III which accept M bayonet lenses (or ltm with adapter). Later Visoflex lenses such as the 280 mentioned, the 400 & 560 f/5.6 and f/6.8 lenses and the rare 800/6.3 as well as a ton of macro stuff. Here are some of my macro items:
http://gallery.leica-users.org/v/hwulff/Stuff/IMG_1438.jpg.html
Gary Elshaw has put together some info which I never properly assembled. Go to:
http://elshaw.tripod.com/ and click on 'Visoflex' in the left column.
I don't have a NEX camera, so don't know what adapters are available there. On the m4/3 cameras I usually use combinations such as: Visoflex III lens (which means M bayonet or 200/4 with OUBIO/16466, Visoflex to Leica R adapter, and Leica R to m4/3. This sounds like, and is a lot but once you have a bunch of adapters lying around, adding one more seems to make sense.
If you don't have any adapters, you could try stuff like finding a 5cm ltm extension tube (Canon used to make those, as well as others) and then using an ltm to m4/3 adapter. if I recall the thickness of the Viso I was about 62mm, so another ring of about 12mm would be necessary to have the distance scale be correct. If the correct rings could be found this would be the lightest solution.
Then there are other solutions, like a OUBIO, a Viso M to Nikon adapter and Nikon to m4/3. This would be cheaper to buy than the Leica R route, and most likely lighter as well, since most of the stuff made for the R system is heavy and expensive, including adapters.
I have all the above possibilites as well as some others including going over the EOS adapters. My favourite and most used is mounting the lens on the Bellows II and mounting that with an M to m4/3 on the cameras. The Bellows II are extremely sturdy and quite easy to use handheld, and this of course allows very close focussing which the Telyts handle very well.
Henning