At 30, I had crooked, overlapping top front teeth and some mild over crowding on 4 front bottom teeth. I was told I would have 17 trays and finished in 14. You wear your final tray for 2 months to help set your teeth, which are used to moving.
I had absolutely no pain, and there was only one tray that ever felt tight and weird in my mouth. I had no filling of teeth and I never had to file down my trays because of roughness. The only con is that they are Near Impossible to remove with attachments. To help with this get yourself an Aligner Remover Tool called an Outie. On Amazon for a set of 3 for $5. You need all 3 so that you can leave one in the car one in your pocket, etc. They are a lifesaver and well worth the cash.
Invisalign are not for everyone. Get 2 opinions, if you aren't sure then just get metal. They don't supply the same pressure as metal, so if you have to close up huge gaps, or pull teeth down out of your gums then just get metal.
I was told in the beginning that almost everyone has to stop 70% of the way through and get new molds taken and different trays made because teeth don't always move according to the molds already made. I did not have this problem and was told I am an exception to the rule.
I wore my aligners 21 hours a day and it will be about 9 months of time. I would absolutely have gone crazy for any more time than that. If your ortho says any longer than a year then go with metal.