[Kraftwerk]

Before merging all my duplicates, I just want to make sure I'm doing it right.

I tested it on one pair of duplicates:
I chose 'merge into first selected book - delete others' which seems to be what I want.

I understand what 'merge only formats into first selected book - delete others' means concerning the formats, but what happens once the formats have been merged?
Just one cover is used and the other deleted? Anything else happens that I need to know about?

If the above is the case, I think 'merge only formats into first selected book - delete others' will work better than my first choice I tested with.

And what actually happens when I add a book to my reading list?
When I connect my kindle it will automatically send the book to my kindle.
Will Calibre pick .mobi as the book to send each time?
How will I choose which format will be sent to my kindle, if for instance I find .mobi of a book is corrupted so want to choose the .epub format that I have merged?