Well after discovering the difference between fixed format and free-flow with my kindle e-books I have to admit that Smashwords offers much to consider as their format and the suggested tools to achieve it have helped to get my e-book formatted properly for both SW and Kindle free-flow formats.
Now, my e-book has one format but two different versions to allow for a difference in copyright pages to acknowledge the distribution by KDP and SW. Unlike KDP, SW also has an ISBN associated with the e-book.
Fortunately for me this also means far less maintenance as I only have on e-book to edit as necessary.
While several marketing channels do overlap, I have been able to opt out of those that KDP will have my e-books in to avoid confusion (hopefully).
Going forward I will continue to use both distribution methods as a way to ensure that those on platforms outside of what Kindle can accommodate have an option to get my book and enjoy it.
The verdict? Two thumbs up!