I had a bad cross bite with 1 tooth completely behind my front teeth (so I looked toothless in photos).
I was given 19 trays (top and bottom). I'm on my second to last tray now and no one can believe how fast the time has gone (9 months) and how fast my teeth have become near perfect.
In the beginning the fact you have a foreign object in your mouth causes you to talk a little funny and even look a little funny... but by the second tray you are a pro. Pain wise- it's sore for the first 1-2 days of a new tray, but its really nothing a few advil cant take care of (Im sure reg. braces are the same pain).
It's really worth every penny, best investment Ive made!