M/M Romance does fairly well in Amazon's Kindle Store. That's the only place I'll go for free books that I hadn't agreed to review for an ARC. Kindle Select (for readers' Kindle Unlimited subscription service) requires that your books are exclusive (ie, not shared anywhere else), but you don't have to use Select/KU to put ebooks up on Amazon. Kindle Create makes formatting and uploading a .mobi file easy. You would need to make sure you have the rights to the cover art.