What would be handy is if we could beg the dev team for a configurable textbox in the "Developer settings" that displays the default user agent string, and has a toggle button that would let you select "Custom useragent string" and supply a custom value if desired. Or toggle to return to "Default value" later, if needed, in case a custom useragent experiment fails miserably.

Of course, there may not be much demand for this. I suspect many users, like me, aren't using the included browser enough to make it worth while. I find the experience of trying to use anything other than the ereader app on these e-ink devices to be so frustrating, I just don't do it anymore. See my post in the Android section about updating my Nexus 7 to Android 8.1, and then using the "reading mode" (grayscale) setting. IMO, THAT is the way to go if you really want a nice Android-based reading experience, and can still run real Android apps and browse the web with no limitations.