What are some alternatives?
When comparing Comixology Unlimited and Marvel (Comics) API, you can also consider the following products
GlobalComix - Professional Comics Publishing
DC Universe - The DC Comics streaming service w/ original content
Piperka - Webcomics listing and subscription manager
LINE Webtoon - LINE Webtoon is a digital comics platform with various comics for free on web and mobile.
Marvelous DB - All the Marvel characters in one searchable place
Tapas - Tapas – Comic, Novel and Stories is free to use digital comic application by Tapas Media that puts tens of thousands of comics and web novel on your mobile device.