The big caveat is that Amazon wants you to enroll in the Kindle Unlimited program—and they'll require exclusivity. This is, to be extremely generous, a bad idea for the author.
Not a requirement that you participate in Kindle Unlimited to sell Kindle ebooks, but Kindle Unlimited requires Amazon exclusivity. (I could have worded that comment better.)
Sure, it is an easy process but you get a lower royalty from Amazon if you are not exclusive for them. My books sell better on lean pub, but I have also started publishing via the Kindle platform.