The cdecl site is intended to explain declarations, and I find it helpful for that. It is not a full C interpreter. It can only parse a single declaration, not a list.
Yes, indeed. It works perfectly fine for single declarations and is not meant for anything more than this.
It's not a "toy". It can be useful not just for understanding "complex" declarations as a human, but also to check your own parser/analyzer, if you're implementing one, against tricky declarations. I did use it at some point for that.
The additional point of this site is to show how absurd C declarations can be, if you want to have a laugh, or if you are considering designing a new language and get convinced that the C syntax is flawed for humans.