They are kind of the opposite of each other. Slow cookers are just that: set it in the morning before work, come home to a slow-cooked bit of meat and veggies. Instant Pot and pressure cookers in general rely on the fact that water under pressure boils at a higher temperature than at sea level pressure, so it cooks things faster. For example, lentils might take 45 minutes on the stove, 10 minutes in a pressure cooker.

In summary, slow cooker->I’ve got time to wait, make the meat fall off the bone; pressure cooker->45 minutes for lentils? Who’s got that kind of time?