A semi static recurve limb holds it's shape in the recurve portion of the limb until the tail end of the draw, then opens up slightly... Some of them open up a little bit at a time through the course of the whole draw cycle....
A true static tip RC holds the shape of the recurve tip all the way through the draw cycle..... This provides more leverage, a better looking DFC chart, and better string angle, and.... It stores most of the energy in a shorter portion of the limbs over all length.
The static tip limbs are typically quieter than a standard RC because the string rolls back up on the hook without string slap commonly associated with a working recurve limb....a bit more preload at brace has a bit to do with that too.
I need to get some high speed video taken on these new SS limbs.
I would be very interested in some feed back myself on the advantages of a semi static tip RC, over a static tip limb....i couldn't give you one myself....