I just got into the visoflex world, and I'll likely only ever use it with the bellows for macro work. I have a 135/2.8, so I picked up the bellows adaptor 16598 for the 135/2.8. When I got the bellows from Keh, the description said it came with the standard 16558 adaptor, but, in fact, came with the bizarre 16570/16590 combo for the 135/4.5 lens head. I picked up a 90/4 screw mount from Tamarkin (not many actual Leitz lenses go for $120 these days) and found an ebay seller with the correct 16558 adaptor for only $22, so now I can use the 135/2.8, 90/4 and, if I ever got them, the 90/2 or 90/2.8 lens heads or 65/3.5 with the bellows.
My only SLR is a Mamiya 645E medium format camera for which I have the 120/4 macro lens, so if I want to do some macro work, the visoflex/bellows setup is strangely more convenient and lighter than either the Mamiya or large format.
It can be confusing to figure out what adaptors to get with what lenses. Since I already had the 135/2.8, I decided to concentrate on getting items to work with it. I still don't have a focusing helicoid for any lens, and I'm not sure if I'm going to get one. I did buy one for the 135/2.8 from Keh when I got the Visoflex and bellows, but it wouldn't mount on the visoflex, so I sent it back.
The bellows II are really nice for macro work. In addition to precise focusing and a lockdown, you can move the whole camera forward and backward with another knob, which helps for precise framing.
Some useful pages:
(see lots of links at the bottom)
A few more, including manuals (I should give the guy a dollar or two for his scanning and posting work).
And here's the results of my first roll of film with the 135/2.8 and bellows, as well as some shots with my 90/2.8 or CV 75/1.8 direct on the visoflex, plus a couple iPhone pics of the setup: