Yes, count me in as a buckwheat pillow adherent. Best thing I ever did to improve sleep. Prevents a hot and sweaty head. Plies into desired thickness or contour well. Apparently, they're also less likely to foster mites or other pillow dwellers. No concern about foam off-gassing.

I have one cased with cotton on one side and wool on the other. The wool side is less crunchy but warmer so I prefer the thin cotton-on-buckweat feel by far.

A king-sized buckwheat pillow is luxurious but weighs a ton. For travel or camping I take a very small version, also useful as a meditation zafu.

Plastic versions of buckwheat filling I've slept on in Japan probably make extra sense in a commercial setting because I assume the whole thing is easily washed and dried. Slightly soft tiny hollow tube cuttings is the best description I can give.

Your rock pillow is interesting. Polished little stones in a thin sack?