yes! for headless/server type applications I think this is the sweet spot right now. In the US, Ameridroid is faster than ordering direct from pine64 (in my experience).

The biggest downside for me is Rock64 doesn't have an OS with the pedigree of Raspbian. I'm running the 'ayufan' minimal ubuntu xenial, and it seems solid. but when I've played around with a monitor in the full xenial build I've seen some crashes and lockups.

Is there a stable Os for it that gets timely security patches etc? (Not that Raspbian does too well here either..)

Arch Linux ARM! https://github.com/m01/rock64-arch-linux-build (it's literally generic aarch64 arch, no more "for this board")

and really any Linux distro can be installed like that

+ "soon", FreeBSD (possible to boot already, but very few drivers have been already written https://lists.freebsd.org/pipermail/freebsd-arm/2018-Februar...)