When comparing Chromium OS vs FydeOS, the Slant community recommends Chromium OS for most people. In the question“What are the best Linux distros that don't use systemd?” Chromium OS is ranked 35th while FydeOS is ranked 51st. The most important reason people chose Chromium OS is:
Since you only have the browser, you cannot install applications (outside Chrome Apps which are decently protected by their limited API and the Chrome Web Store). This means no harmful virus, and also nearly no way you can screw your system. Everything will just work.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Safe and requires little to no maintenant
Since you only have the browser, you cannot install applications (outside Chrome Apps which are decently protected by their limited API and the Chrome Web Store). This means no harmful virus, and also nearly no way you can screw your system. Everything will just work.
Pro Minimalistic interface
Chromium's system UI uses as little screen space as possible by combining apps and standard web pages into a minimal tab strip: While existing operating systems have web tabs and native applications in two separate strips, Chromium OS combines these, giving access to everything from one strip. The tab is the equivalent of a desktop application's title bar; the frame containing the tabs is a simple mechanism for managing sets of those applications and pages.
Pro Lightweight
Because Chromium OS is designed for users who spend most of their computer time on the Web, it is intended for use in computers with little local storage and fast boot-up times.
Pro On par with Chrome OS
Features are almost on par with Chrome OS
Cons
Con Google
Possibly harms your privacy.
Con Made for developers
ChromiumOS is mainly made for development, so there exist no official install images and you have to build it from source or use third party images like Arnold's or the waterfall images.
Con No auto-upgrade (unlike Chrome OS)
Chrome OS auto-upgrade the system, but Chromium OS does not. It's possible that they're thinking about adding that feature from the design doc.
Con Chinese Software
You never know... ...they also replaced the Google cloud with their own(but you can also revert this back (https://forum.xda-developers.com/hardware-hacking/chromebooks/fydeos-google-sync-using-fydeos-account-t3872442).
Con No dualboot
It does not support dualboot on the same harddisk as the OS.