It's great to see all this attention to New Tribe Saddles! All three of these are in our "heavy duty" or "work" class of saddles, which means they all have the beefier belt pad and extended legpads that make for more comfort time during the day. This is especially important if you are a large, heavy person, are working, or are doing some intense rigging (setting multiple ropes or multiple Treeboats, for example) on a rec climb. Otherwise, if you are a casual recreational tree climber, you'll be happier with our lighter "Basic" or "Side D" saddles. They are so light you forget you have them on, and they're all you need for safety and comfort on rope.
The main difference between the three models you are asking about is in the "bells & whistles." If you like snaphooks and rings for clipping in tools, choose the Work Saddle. If you like Big D Rings and don't mind a heavy harness, choose the ProGear. If you're a rec climber who wants a serious working saddle that's also comfy to kick back in, then the Vi Special is your best bet.
This is the first year that we've produced a saddle with "soft" Ds, built of webbing and nylon canvas instead of steel. We use this feature in the "Ultralight" that you see in Sherrill's 2005 print catalog. Tobe Sherrill worked with us to create this model, and for the first year you will only find it from Sherrill. That's why it doesn't appear in our New Tribe catalog or website. Look for a recreational version of this directly from New Tribe, beginning sometime in Spring, 2006.
High and happy,
Sophia