When comparing Netlify CMS vs Flextype, the Slant community recommends Flextype for most people. In the question“What are the best open source headless CMS's?” Flextype is ranked 2nd while Netlify CMS is ranked 6th. The most important reason people chose Flextype is:
Define unlimited custom fields for any of your entries.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Experimental support for GitHub's GraphQL API
Experimental support for GitHub's GraphQL API is now available for the GitHub backend. Without mutation.
Pro Easy Creating Custom Widgets option
The NetlifyCMS exposes a window.CMS global object that you can use to register custom widgets, previews, and editor plugins. The same object is also the default export if you import Netify CMS as an npm module. The available widget extension methods are listed here.

Pro Modern

Pro Open-source

Pro Built in React.js
Pro Dynamic Content Types
Define unlimited custom fields for any of your entries.
Pro Free
MIT-licensed open source project and completely free to use.
Pro No external DB required
Pro Built-in REST API
Provides APIs organized around Representational State Transfer (REST) for working with content.
Pro Version Control
It is easy to version control all content in Flextype with GIT or any other Version Control System.
Pro Flexible
Simple but powerful Core API's.
Pro Super Fast
Elegance architecture and built-in smart cache.
Pro Tokenized API
Cons
Con A lot of configuration
Example: a few plugins and some code are needed for gatsby-img or markdown to work.
Con Same CMS repackaged
Same CMS that got regurgitated over and over for years.
