My son bought one that wasn't a known brand, which didn't last. My Roomba is as good as new.
You do have to empty the rather small dustbox pretty often. They say to do it every time it is used, which is a bit overkill, but if you leave it too long it drops more than it picks up.
You also have to watch out that you don't leave thin fabric trailing on the floor - a scarf for instance - as it gets caught in the brushes and the robot then shrieks for you to come and rescue it.
I was inadvertently very cruel to mine. I had it scheduled to sweep most of the downstairs carpets before I got out of bed, but forgot to firmly close the door of the one room it wasn't to go into. When I came down, I found that door was closed, and the desktop computer in that room wouldn't work, though I tried everything. Then I saw Roomba, huddled dejectedly in a corner. My first thought was that there had been some kind of electrical disaster, but no.
It seems it could push on the outside of door enough to open it a bit further and get in, then it hoovered diligently until it came up against the extension lying on the floor with the computer plugged into it and ran over the switch on that, turning the computer off. After that it must have continued vacuuming until it came up against the INSIDE of the door and pushed it closed. Then, of course, it couldn't get out to go home to its recharging station and switch itself off, and could only keep on sweeping until it ran out of power and had to wait to be found.
After that I was very careful about whether doors were wide open or completely closed.