Here is the sales pitch from the website
POLYAMIDE 66 THREADS
Polyamide 66 Threads are made up of macromolecules with repeating units liked together by much stronger amid bonds (Chemical Bonds), rather than other threads that are held together by ester bonds.
These threads show high elasticity more than normal polyester and nylon threads that are more commonly available in the market. Therefore they are more suitable to sew curved shaped pieces of leather, vinyl or fabric without any signs of ungainly puckering and corrugations at the seams.
They have the properties of well wear resistance, high strength and controlled stretching, and are UV resistant, repel moisture and also color fade resistant. Due to these unique properties these threads have become very popular among various industries. They are preferred for stitching multi-ply leather gears and because the continuous filaments are tightly twisted and packed together. When in cross top stitching (French Stitching) the needle will not enter the center of the other top stitches and create a very consistent and uniform French Stitching when finished.
So I guess it is time to just jump in and try it.