...or rather the lack of a convincing one? The idea of playing in a tremelando manually (ie: rapid note repetition) doesn't work for me, though the principle is sound, since one could be in total control of the tempi. But it's a lot more complex than that on a real violin. I had my doubts on one of the demos, which contained it, and it was conspicuous by its absence in the demo articulations. Now that I have the Stradivari, it confirms my feelings. Realistic tremelando isn't (yet) possible. It seems an odd decision not to include sampled tremelandi, that could be keyswitched. I'm also reserved about the trills being manually executed: they don't quite cut it for me, but, again, it's a great idea, and I admit it's early days, both in my experience and in the life of the instrument.
So far, though, the manual playing of trills does not, to my ears compare well to sampled trills. Other aspects of this instrument, however, are outstanding, and it has already enhanced the string sections of two other heavyweight libraries (which will remain nameless) that I use.
I'm looking forward to the release of the remaining strings and the expansion of this technology into the rest of the orchestra, including sections, too.