It's just big enough that it might be barely usable to touch type with sufficient practice, not comfortably though. Definitely seems smaller than the Libretto from glancing at pictures. If the idea is to have a portable keyboard to then sit down somewhere and work, there are pocket BT ones that fold in half and are comfortably big.
The only use-case I can think for the Pinephone keyboard is if for some reason you want a physical keyboard to use while walking.