The free ISBN is no bargain when you consider that by purchasing ISBNs 1,000 at a time POD publishers can get them for $1 each. And, the larger POD publishers who purchase 10,000 or more can get them for even less than a dollar. When a POD publisher gives you an ISBN free, they are purchasing your right to take your book to another printer for under $1.
This can be important and it saved me $3 per book on my first POD project. Had I not owned the ISBN I would have been stuck with the higher price and reduced profit.
To protect your investment of time and money in your book, purchase your ISBN for Bowker, Inc. at: https://www.myidentifiers.com/isbn/main .
One ISBN will cost you $125 but for $250 you can get 10 ISBNs and for $575 you can get 100 ISBNs. As a small publishing company I purchase 10 at a time and if you have any intention of writing more than one book or ebook, I suggest you do the same.