I'm not sure that these would be described as simple - perhaps to use, but not to build! You might also want to use the STEM tag for this kind of topic.
I have a Roomba but it's not perfect. It sometimes gets stuck under furniture and doesn't always make it back to its charging port before its battery runs down. And it has a very small bin. But it does pick up well where it does cover! Perhaps the newer ones work better...
I'd love to have the lawnmower if it wasn't so pricy!