Have used one, a Roomba, for some months.
Obviously,being circular, there are edge areas which occasionally have to be covered with a conventional cleaner, but but only very occasionally (like once since February).
Our method is that for a routine clean we switch it on when we go out and it does its thing for an hour or so. Every so often, for a deeper clean, we prepare the room a little, make sure all wires are out of the way, and there are clear paths.
Because the dust compartment is small we find little (like one or two rooms at a time, rather than the whole floor) and often the best way.
Much of the criticism of these cleaners is due to over expectation.
If you have a dining room table with four chairs tucked in around it do not expect a very good clean under the table!
Used it earlier today and if it had broken down I would have already had a new one on order from Amazon.