But a couple of cool things about Roombas: they automatically redock with their charging station; and they come with a couple of "walls", little battery-powered boxes that provide an infrared barrier that the Roomba won't cross, allowing you to keep the 'bot out of a room or restrict it to certain areas.

The engineering of the Roombas is pretty clever. They use some kind of pseudorandom navigation to maximize the coverage of any size and shape of room and they mostly deal with obstacles and furniture amazingly well. That said, my Roomba does very occasionally get caught under one of my sofas or trapped by the crossbar of one particular chair. In either case it complains audibly then switches itself off. As this is wont to occur in the wee small hours, I get to play find the 'bot about once per week.

Emptying and cleaning the Roomba is easy and it is always shocking how much crap has been sucked up, even in an ostensibly clean room. Yuck.

The Scooba is another matter entirely. You fill up its tank with water and vinegar, or water and a special cleaning solution and it runs around wetting the floor and sucking up most of the liquid along with the dirt. It does an OK job but every fluid option I've tried has resulted in streaks on my wooden floors.

Now, it is true that my floors have a shine that tends to make streaks highly visible and, while there's no doubt that the Scooba is actually cleaning the floor (the amount of dirt in the onboard tank at the end of a cleaning cycle is, well, seriously gross), the aesthetic results are disappointing and call for a follow-up manual mopping which rather reduces the value of the Scooba.