I've been boycotting Kindle for quite a few years now, so I genuinely don't know what that experience is like now. At least the last time I used it though, there was a pretty clear difference between my epubs and Kindle-provided content in the way the UI treated it and the user experience when consuming it. Are they fairly equivalent experiences now?
I use the Android phone app for Kindle. Sending an ePub to it using the Windows "Send to Kindle" program[0] is really easy, and I don't notice any different user experience in the phone app when I pull up my library.
Yeah. It’s been improving slowly for a while but it did seem to pick up just before they announced the scribe. Uploading your own documents to be able to mark them up is a key differentiation and it would have been panned if that wasn’t synced