It is mainly UX/UI and the integration of hardware and software. Android quite often ends up feeling clonky because of it being slow. Additionally the UI difference between Apps and phone brands is really weird in some cases. At least that is my experience

It has helped me get a good indication of my heartbeat and helps me tack sleep, which in tone helps my GP gain some insights in to my health. But besides that I would actually prefer to go back to a normal watch.