Just my two cents: Mirage is freaking great because it makes mocking shit out pretty much as easy as possible and pretty damn correct.
I don't know how many times mocking up a UI I start to throw some random JS objects in a file and then inevitably after a few hours, those random JS objects are unmanageable and contain very small differences between what my API will deliver.
Using Mirage from the start of projects has made my life a lot easier, it also provides a nice sanity check between what the backend delivers and what the frontend actually expects.
I don't know how many times mocking up a UI I start to throw some random JS objects in a file and then inevitably after a few hours, those random JS objects are unmanageable and contain very small differences between what my API will deliver.
Using Mirage from the start of projects has made my life a lot easier, it also provides a nice sanity check between what the backend delivers and what the frontend actually expects.