If you want a cheap rooted eReader I think you're better off getting a Kobo instead, they don't officially support rooting but AFAICT they make basically no effort to prevent it.
The latest Kobos use MediaTek SoCs with locked bootloaders. The Kobo Clara BW's MT8113, for example. As far as I know, one of the early bootloaders it, BL1, refuses to execute the next bootloader (BL2) unless its signature is valid. We can get the device into a mode where BL1 waits for upload of a BL2 via USB using an exploit called Kamakiri, but in public there is neither an exploit to get BL1 to boot an arbitrary BL2, nor an authorized BL2 image to upload. See here: https://github.com/bkerler/mtkclient/issues/1332
Kobo devices have root exposed but don't let users boot their own kernels (and the kernel they ship was not compiled with kexec either).
I really don't know the reason so many devices these days don't have an unlock method. It seems predatory. Who knows where in the chain this happens... maybe it's Kobo, or maybe MediaTek won't sell you their SoCs for mass-market devices unless you lock them.
According to the github issue it seems to be a simple checksum step, not a true signature verification? If so there is no locked bootloader in any real sense.
If the real impediment is lack of demand or low-level development effort for any given device, that's in principle a solvable issue once projects like pmOS and Mobian choose to focus on some reasonably-available hackable hardware and bring it up to true daily driver state.
mtkclient does not seem to correctly interpret the usb output of the device past some part of the early boot process. Really, any of those messages formatted by mtkclient are unfaithful to the intended meaning. So yes maybe it is "just a checksum step" or maybe something else entirely. Last year I collected some UART logs on the device during bootup in a zip here:
As far as I know, yes, it's possible. No SELinux. Kernel is a branch from 4.9.something pretty far off mainline with a few proprietary binary blob modules. As far as I know the real impediment here is lack of demand.
+1 to a Kobo, they cheaper and better than Kindles, with full Calibre support (https://github.com/kovidgoyal/calibre - OSS which has been in development for ~20 years!).
The way you install additional software is literally just moving files into folders whilst its plugged into your computer. I'm sure it could handle Tailscale.
I agree with your sentiment that the Kobo is better than the Kindle from an... ethical standpoint, if you have the money for one. However, it is worth noting that Kindles will always be cheaper than Kobo devices [0] due to economies of scale and lockscreen advertisements (removable with jailbreaking). From a pure cost perspective, and assuming the user is technically-minded enough to accomplish the jailbreak, the Kindle is likely always [1] a better deal.
[0] as of today, 12/8/25, the "base model" Kindle 11th Generation is priced at $109.99 USD, and the respective Kobo Clara BW is $139.99 USD.
[1] I say "likely always" to cover my bases. To my knowledge Calibre supports Kindle, just not as well as Kobo. That said I have found that the KOreader app is more than powerful enough for my use case (reading my own epubs, using dictionaries, etc.)
Where do I get DRM-free ebooks to put on a Kobo? I don't support breaking DRM. So I'm using a Kindle because it has the best access to and integration with almost any book I want.
I kinda love that buried in the koreader menu somewhere is an option that drops me at a linux shell. I have no use really for this feature, but i like it. Good for those times you absolutely have to crank out some awk on the plane or whatever. :)
Same with the Barnes and Noble Nooks. I've never rooted one, but via ADB one can install a launcher and most Android applications run. I've used four generations of Nooks to run AnkiDroid.
Just beware to check what version of Android the Nook is using before you buy, and what your app needs.
I used to like my Kobo a lot but recently it's got some pretty severe unreliability issues, usually around reading non-Kobo epubs and PDFs. Like, if I open of those files, the device usually crashes and when it recovers after a reboot, the file disappears.
The only (tiny) issue I've had with Tailscale on Kobo has been that the tailscale daemon prevents me from using the Kobo in Mass Storage Mode while it's active, so I have to disable/quit KOReader to be able to plug it in again, which is admittedly not frequently warranted anyways.
Resell it, or wait six months. FWIW the 10th generation Kindle Paperwhite (the "PW4" in kindlemodding/mobileread lingo) doesn't have as large a screen as the newest models, but its maximum supported OS is currently 5.18.1 (and you can download that update directly from Amazon and transfer over USB), which is vulnerable to AdBreak. I just jailbroke and Tailscaled my PW4 this weekend after numerous failed attempts over a period of about a year to use the previous WinterBreak exploit.
I read mostly on my iPad; the Kindle is really just for reading outside, like at the beach/pool. But it was such a neat idea that I couldn't just pass it up.
There is a new jailbreak, that is currently unpatched. You might need to make sure your Kindle doesn't get updated first by filling in all the disk space.
Bought one from eBay to try it out. Silly me connected it to wifi and suddenly it’s up to date and no longer breakable