Not sure about a hudl but on my kindle for iPad I have two options - cloud and device. Everything I down load is on the cloud but I have to actually load on to my iPad to read them and then they are on the device. This means that I can read the same book from two different devices. So if you were going somewhere with no internet access you need to make sure anything you want to read is on the device. I always delete them from the device when I have read them, but they are still on the cloud if I want to read again. Amazon also tells you if you have already bought a book which is useful.
I find recipe books are not so good, it is not easy to flick back and forward you have to use the index.
Look out for free books, lots of authors offer them in the hope you will buy their other books.
I have just read Best wishes sister B by Fran Smith who is a gransnet member, it was very good.
I think you can put a book you have read into Archive and get it back if you feel the need to reread it. Mine is a kindle and to be honest I'm still finding out about it although I've had it a good few years. Books which haven't worked well on kindle are poetry books and factual books where I want to jump from page to much further on.