An automated estimate reads public records and recent sales in your ZIP code. It does not know what you did to the kitchen, which side of the street backs to preserve, or what the last three homes on your street actually closed at after concessions. This is the other kind of number — worked out by hand, for your address, and it comes with the costs subtracted rather than left out.
Nothing here is submitted to a server. The button opens a message in your own mail app with these details filled in, and nothing is sent until you send it.