Just to add my 2 cents (Canadian) into this discussion, I did some downloading, browsing and returning Kindle Unlimited books. I reached 374 before I gave up and did not manage to trigger any warnings from Amazon. Basically, borrow book, read first couple of pages, scroll to end, read last couple of page and return. Repeat until boredom set in. It was something to do over a couple of boring evening while monitoring the MAN.
All I can say is those 374 randomly selected books made it very easy to believe that KU nothing more than a massive slush pile full of copycats.
See
The shocking truth about the slush pile.