I got the dates wrong, so I fixed them above. A comment asked about which ones are best suited for which sort of use. Simplistic overview follows:
- Space Navigator - simplest unit, and least expensive. Navigation and two buttons ($99)
- Space Navigator (travel/notebook) - same as above except smaller but a bit more expensive ($129)
- Space Explorer - More features, programmable buttons, hand rest ($299)
- Space Pilot - MCAD optimized with even more features, including a small user interface screen that provides access to email and more ($399)
Assuming I could actually try one with Revit I'd probably focus on the Navigator or Explorer. It's hard to say if the price difference for the Explorer is justified without living with them for awhile. I'd guess that the extra buttons would earn their keep if you are are accustomed to remembering to use them. I find I don't remember some of the keyboard shortcuts I make or the extra buttons on the Intous 4 I've been using. So I might not ever remember to use them and if true I'd probably be better of with one of the Navigators.
I should add that they are intended to be used along with your mouse (pointing device). The dominant hand drives the mouse and your other hand operates the 3D Connexion device. Just ask yourself which hand holds a piece of paper when you use a pair of scissors or hold a piece of lumber while using a saw. Same kind of automatic brain mapping to the 3D Connexion devices occurs pretty quickly.