These books should be usable on any Kindle or Kobo device. Just be sure download the appropriate format for the device - the download page on this site will tell you which one you need for your device.

Personally, I use a Kobo Libra 2. Not the cheapest ereader at $179 USD, but I went with it due to USB-C, IPX8, and support for the third-party KOReader viewer.

I recently need cheap one and got Pocketbook Touch HD 3. My expectations were low but it turned out to be great. It runs their locked down linux distro but it had Dropbox sync and i installed KOreader on it. Kinda everything i needed.

I have a KOBO Libra H20, it is very good. I loaded KOReader on to it which adds functionality (https://github.com/koreader/koreader).