Minimed 780g user here, it is not perfect. For a true closed loop we need a system that can give glucagon as well. The current closed loop only gives you insulin to lower your blood glucose. When it gives too much it wakes you up and asks you to treat it. You also have to accurately count carbs of meals you eat, enter when you exercise. The sensors are also not quite reliable so sometimes it freaks out and you calibrate and go manual.

For a closed loop we need insulin and glucagon in conjunction to keep the bg stable without user intervention.