User of the MAC liked to eat over their keyboard. Some keys didn't work, some liquid spills and food found inside. It is not a T.V. tray for God's sake...
I am a PC repair guy. First time fixing a MAC. Nearly broke the release for the keyboard ribbon as it releases differently than what I found on PC laptops. I only broke half of it...so it still works. There are a million screws to remove. All told, probably took 1 hour. First time is a charm...now I know what I am doing.
Take your time...if you get stuck...think it through. Careful with the ribbon releases...make sure you know which way they release.