Apigility is loyal to the standards; we do not need a framework to write custom REST APIs, anyone can do that; we need a framework that makes sticking with the standards easy.

Every PHP framework should be designed in such a way, that it forces you to think about what you are doing, the current PHP mind-set is too much crowded with lazy documentation of custom-solutions that do not work as expected (because the language gives you too much freedom).

With Apigility it is easy to build RESTful APIs in a declarative way, so that you do not need to write tests for every API Service you create, because the underlying code doesn't change or break, all functionality comes within the framework, that has already been tested.

You do not need to write any boiler plate code, which is huge plus compared to Symfony 2 and the likes.

Apigility has had some reliability problems with newest releases and as far as I know, they do not report which release is the latest stable. But of course, they reached the 1.0 in 2015.