FramerJS is great for creating prototypes you can then test on a mobile device. I played with Quartz composer a while back and at the time there was no way to use the resulting prototype on a mobile device, which I found to be counter productive. I'm not sure if this is still the case.
Also, as Koen mentioned, you are using existing skill sets for front-end development (HTML, CSS, Javascript) meaning anything you learn whilst building FramerJS prototypes can be applicable to front-end dev and vice versa.
FramerJS is great for creating prototypes you can then test on a mobile device. I played with Quartz composer a while back and at the time there was no way to use the resulting prototype on a mobile device, which I found to be counter productive. I'm not sure if this is still the case.
Also, as Koen mentioned, you are using existing skill sets for front-end development (HTML, CSS, Javascript) meaning anything you learn whilst building FramerJS prototypes can be applicable to front-end dev and vice versa.