The XV-11's physical collision detection system works well for most objects it encounters but the laser turret turns out to be a problem. The device's shape (rounded on one end) is designed to make it highly maneuverable and allow it to actually get into corners (something that the Roomba's circular shape can't do as well).

But here's the thing; if the XV-11's body is low enough to pass under, say, a chair's crossbar there's no guarantee that the turret will also be low enough to avoid getting caught. As the turret has no collision detection and the XV-11 has some pretty musclely motors, one of two things will happen: Either the XV-11 will stop and complain that it's trapped and go to sleep or it will drag the chair around. This happens with some bar stools I have; I set the XV-11 going and came back to find the stools had all been dragged around the room after which the XV-11 had got stuck under a sofa.

The XV-11 can be constrained by a "boundary marker", a strip of plastic that you lay across a doorway or anywhere else you want to keep it from entering. Compared to the iRobot "walls" this is a clumsy solution.

Another problem the XV-11 has in my house is fringed carpets: About half of the time the XV-11 will roll happily over the fringe while the rest of the time it will suck the fringe into its vacuum system and stall out, sulking until it gets freed.

There's no doubt that the cleaning power of the XV-11 is excellent (the dirt in the hopper even after a short run qualifies as embarrassing), but its inability to avoid getting trapped under the couch and its demented rearranging of my bar stools makes it, at least in my house, a non-starter.