We have had the shark for about 3 weeks now.  It seems to work great. It does go back over some of the same area, which is fine do don't watch it. We have a basement and the shark stops at top of stairs without falling downstairs. It did get stuck once on a throw rug that was not totally flat.  If it dust trash collector gets full it goes back and dumps . It returned and continued on. Overall really happy with it.