It is useful software for offline use and emergencies. For those who may not know, apart from wikis, they also offer offline documentation(Linux distros like ArchWiki, libraries, etc.), medical libraries(Medicine Plus, etc.), and Stack Exchange.
It's an interesting idea. GPD makes machines that will appeal to those interested in handheld gaming and those on pager duty.
I own devices from GPD, and I have had two issues -- devices are simply not reliable, in just over a year the screen showed a green verticle line, and the display died a few months later. Secondly, the keyboard is simply unusable if you plan to program on it.