Do you have any information about comparative reliability? For me, reliability is a virtue second only to "does it work at all?"

I had a Roomba some years ago, the second-series "Discovery" model. I had less than two years use out of it before the cliff sensors started behaving like it was always looking over a cliff. Taking it apart (a very long and fiddly task which left me distinctly unimpressed by its design) and cleaning everything I could get at helped for a while, but not enough and I eventually relinquished attachment to the sunk cost (i.e. I threw it out). iRobot after-sales service outside the US was nonexistent then, and spares were unobtainable.