just bought 1 and it was disappointment buy, the sensor fail to detect on the dark area such as under the sofa, once it go in and is either stuck inside or take long time to come out. Secondly, the sensor unable to detect cliff and kerb, any furniture such as non-four legged chair or table, it will mount onto it and stuck there. Lastly, the sensor unable to detect any cliff infront of it, hence it will just move forward and drop down and will have hard time to come up. Although is cheap, but i wont recommend it. 👎👎👎