Better off spending money on a proper vacuum cleaner.
I can only see these being useful in a big house which is all open plan. Also, even so, these types of vacuums will still miss dust that isn't on the floor. So you still need a cleaner, or another vacuum or will have to dust everything by hand.
On a similar note, I knew some people who had a robot grass mower. It tended to crash all the time, so did nothing. Bizarrely though, it suddenly came to life and decided to start mowing in the middle of a lightning storm!