I've got Kindle on iPad and iPhone and have just tried this. All works as you say but yes, you can edit notes on either and they copy across.

I found it a bit slow but I expect this is an artificial situation: I was holding the iPhone in my hand while making notes on the iPad. Normally I expect I'd do what you do and write on one then later on the other. The latest-page feature is similarly slow if you test back and forth but works perfectly well in natural, normal use.

I should say that iBooks does all this too. Much as I like Kindle on iPhone and iPad, I do prefer the reading experience with iBooks. Oddly, I prefer how Kindle displays the notes, though. Cosmetic things in both cases and anyway both apps are free so I bounce between them depending on where I've bought the book, if I have.

Popping your own material on iBooks has been easiest to do in PDF, though its editing of PDF files is more limited. You could convert your material into the ePub standard and have iBooks treat it as a book but it's been a little fiddly until this week: there's been an update to Apple's word processor, Pages, that makes it simple. If you've got Pages, at least.

I was interested in what you say because I've not made notes before: I've reread on iPad and made highlighter marks on passages I needed to revise yet I hadn't looked into the note taking.

I do somehow enjoy reading my material on iPad - and as soon as I discovered my agent is an iPad fanatic, I made sure I sent him the next material in an iBooks form.