Their definitley way more durable than generic belts. Their a good thing to get if you have aftermarket cams, both from a performance standpoint and as a little insurance.
At very high RPM's, weaker generic rubber belts can slightly flex which throws off precise cam timing. This affects power output of course.
Also all this flexing can weaken generic belts and cause them to fail prematurley. Toda created their timing belt precisely because their Toda B and C cams were tearing up generic belts very quickly. MichaelDelaney on Team Integra can tell you all about his experience trying to get Toda cams not to eat up rubber belts (he couldn't do it), and I knew someone with an ITR who had the same problem with Toda's.
I have aftermarket cams and use a Toda belt. My cams aern't as big as Toda B's, I wanted the insurance anyway, lol.