This is a truly revolutionary design, the unit balances evenly with the weight on the windowsill, so much sturdier and safer than the traditional design. Our windowsill is not flat, but we were easily able to accommodate the unit with the included foam strips and some easily applied home ingenuity (a couple of wood blocks we had on hand raised the surface enough; a couple of decks of cards would have done the same.). I should add that this was in a 90 year old cottage so some home ingenuity is to be expected there!  

The unit cools the space very quickly, and it is by far the quietest air conditioner we’ve ever had. Highly recommend!