Talk to your local pro shop and see if they will let you borrow(or at least return for refund the unused ones) a couple of different versions, then ask your OT which one would be best for you. Then you can purchase that one.

The "mechanical arms" give the most support, but a softer version might be better for you.

I have a weak wrist and the mongoose lifter really gives me good support without the soreness I get without it

 
Agreed on the Lifter. Also check out the new "Wedge Kit" for the Lifter:
 
http://www.mongooseproducts.com/product/new-the-wedge
 
The wedges give about the same cup capabilities as those found on the hard/bulky robo braces. I tested out the wedges today, and they really do provide the best of both worlds -- the comfort and lightness of the Mongoose with the support and leverage of hard braces.
 
But to Milo's point, it's always better to be able to try before you buy. Work with your proshop guy to see what he can do.