[darryl]

The only reasonable way to decide about Kindle Unlimited is for you to give it a try. There is of course a free trial. If you don't have a Kindle you can read on your computer, Android device or IOS through apps, or even in a web browser. KU is not 10 books a month. It is up to 10 books at the same time whilst you are a member. So if you have 10 and you want to borrow another you need to return 1 of the 10. The books are never yours. Think of it as borrowing them. As such you do not have access if you cease to be a member. But how many books do you actually want to keep after you have read them? These are generally not very expensive books, so it is not exactly going to bankrupt you buying the ones you want to keep if there are only the occasional few. The large publishers generally avoid KU totally. It is mainly self-published and books from Indie publishers, including books from Amazon imprints.

Some here will tell you it is good value. I find it so. Others will tell you it is a complete waste of money. You need to make up your own mind.

Adding to Calibre would be a waste of time without removing the DRM. Many Mobileread members are supportive of removing DRM from EBooks you have purchased, but not from library books and similar. KU ebooks fall into the similar category. You should not do it, and no one here will help you to do it. And yes, I know I didn't answer your question.

My advice is to give KU a try.