I can say for sure that currently library books go to my default kindle and there's an opportunity right on the page at the time to then send it to other devices if I want.
I have the same drop down option to pick a device; my problem is Amazon ignores my selection. No matter what I pick it sends it to the default device, except for those unexplained odd times it sends it to my library. Even when the purchase page says it will go to my library, it still usually goes to the default device. Except for a few random occasions when it really does go to the library.
I always download for transfer by USB. Amazon used to honor that choice but suddenly it started sending everything to the default Kindle regardless of what I select on the dropdown. So then I have to go to "MCD" and download; but at least that still works. Having the book go to my library is fine, I don't mind doing the "MCD" download, I just don't like having a truckload of books queued up waiting for me to take a device online. I try to avoid connecting my Kindles to wifi because I don't really trust Amazon not to do things to my Kindles I would rather they not do. Syncing, statistics and all the social media stuff have no value to me.
Wally
