It's working. I've waited a couple of months to deliver a final verdict, because first I spent a few weeks slowly adjusting the amount of fill, and then longer waiting for the otehr shoe to drop, only it never did.

It's not perfect - I actually wish the central dip where your head goes was a little bit thicker. The adjustable part is the bit that fits your neck, there's no way to change the deoth of the hollw, though I suppose you could put a blanket or something under it to lift it up half an inch or whatever. But since I got the filler right, I haven't once woken up with a stiff neck. It's the best pillow I've found by quite some margin.