I've been tying on a dan-vise for about five years now, and still enjoy it. It works perfectly well for anything up to about a 2/0, depending on the thickness of the hook. (by that i mean the REALLY heavy 2/0's might not stay put real well) It works perfectly for my redfish flies, which are the kind of things most people throw at bones.
That being said, if I was buying one today, I would get the Renzetti Cam Traveler. It's all metal, more durable, and i like the bobbin cradle much better. Some might disagree, but i think its design is much more user friendly than that of the Dan-vise's cradle. You'll notice they make a version of the Traveler called the "Saltwater". A better title might be "Offshore" you'll only need to bump up to this one if you expect to regularly tie flies between sizes 2/0 and 8/0.
I find rotary vises to be most useful for saltwater tying. Especially for clousers and decievers, where you're tying bucktail in on different sides of the hook shank. (lefty ties his decievers with three clumps by the way) You'll also find the rotary function helpful with buggers and for some dubbing applications. Here are the opinions of others on rotary vises and their applications: http://www.flyanglersonline.com/bb/F...ML/004258.html