Not the parent comment, but I think it depends on the house you have. I find huge american houses with 3-5 rooms are unsuitable, except when you limit the robot to one or two rooms.

My apartment in Europe is suitable for it, as I do not have many rooms, so that it does a decent job on cleaning. I do not use the regular vacuum very often.

How? I've had a roomba for almost 2 years now, and I use it all the time - it runs and cleans our living room and kitchen at least 2-3 times a week. There has been a noticeable reduction in dust present in the house. And that's not even a fancy self-emptying model, just a normal roomba where I have to empty the bin by hand. Why would you stop using one?