I suppose it's not intended to be a laptop, but rather a "communicator" device as they used to call it a decade, and something ago. Small physical keyboard is worse than a full-size, but better than small on-screen one. At least, as far as me experience go. I did a lot of emailing with Nokia N900 (3.5" screen size, phys kbd), I would not do it on any modern smartphone in spite if them being wider, and longer
The UK's Planet Computers already occupy that niche, albeit with a focus on Android (although Linux can be installed on their Gemini PDA and Cosmo Communicator models): I'm waiting on the (long-delayed by COVID19 factory shutdowns and supply chain dislocation) [Astro Slide 5G](https://www.indiegogo.com/projects/astro-slide-5g-transforme...), which looks like an interesting -- if obsolescent on delivery any month now -- smartphone/keyboard/PDA hybrid.
I would bet that the ortholinear layout and simple button spacebar they put in that device kills any productivity gains you would have with a physical keyboard.
For a device of this size, I would measure productivity gains in terms of accuracy rather than speed. That is to say: I don't expect to type as fast as I would on a full size keyboard, but I would expect to be more productive than I would be with a touchscreen keyboard. Whether the ortholinear layout affects that, I don't know. Admittedly, the small spacebar buttons probably would.
