My experience (Roomba PetSeries595)
approximately three years; two homes; both ~450 sq feet; one child
have never needed to use any other vacuum
I am meticulously neat, and my feet are extremely sensitive to tiny invisible crap on the floor and Roomba does the trick
I run her every few days
I empty the bin every couple of weeks
clean brushes, etc, every few months
enjoy cleaning the brushes, etc, as a peaceful, quiet meditation
have not yet needed to replace the battery
have replaced only the brushes (once); the replacements came with
my floors always look amazing
I also need to mop way less
it's entirely happy to go under tables, around stuff, etc
love that it cleans thoroughly under my bed
it generally goes over or around cords; on the occasion that it "catches" one, it stops itself
the compartment allows you to retrieve lego pieces, etc, if those were missed in a tidy
excellent on my hard (laminate, and tile) surfaces as well as on my carpets (both low pile and thick)
the electronic "wall" works perfectly; I will do my main living area regularly, other areas less so, block an area via a door or e-wall
I adore coming home to such a clean place over and over!
When my landlords saw the results, they got one too :)
When I moved, I only brought what fit in our compact car with us. Roomba was a shoe-in.
Agree that small things need to be picked up first. Here I also have grate covers for some of my baseboard heaters that sit a couple inches off the floor. I remove those for a clean under the heaters, so it goes all the way under and also doesn't get stuck. I find "static things that hang about 2" off the floor" the only vulnerable spots that way.
I am wary of the "cheap" ones. I wouldn't bother with one less awesome than what I have.