FR24 is a commercial site founded by a couple of Swedish aerosexuals. It's basically an enthusiasts site. Anyone can contribute data, and anyone can request their data be blocked ie their aircraft don't appear on it. I'm pretty sure there would be no checks as to how accurate anything displayed on it is. We use it at work, but only for very basic information. I wouldn't base any sort of traffic info on it, as there is no way to know what it should be showing vs what it is. Stuff appears and disappears all the time.