I borrowed a Kindle Keyboard in order to test the Send to Kindle feature in L6, as I really want to find a device with that type of display that I like, and that does not give me a headache. The last device I tried was the Onyx t68, which has various issues that make it useless.
My biggest complaint was that when I clicked on a footnote, I was jumped to the list of footnotes instead of having a popup. I still liked it enough that I decided to purchase a Kindle Paperwhite, and to my pleasant surprise, the footnotes display in a popup!
Also, since I had linked the borrowed Kindle's email address to my L6 account, I was looking at having to call customer service to get the email address changed for the new Paperwhite, but when I unregistered the borrowed device, I attempted to immediately change the email address of the Paperwhite to the address already associated with L6, and it allowed me to use the same address (it actually stated that it could take up to 24 hours to release the old email address, but it was instant).
I just thought this might be useful information to anyone wanting to utilize this feature. I have been enjoying reading my Logos books on the Kindle device.