I had braces for 18 months on upper and lower teeth. They came off in September last year. My teeth were crooked at the top and squashed at the bottom and I had an overbite. My (very good) dentist recommended an equally good orthodontist to me and I'm so pleased I did it.
I had clear braces (well, clear brackets with metal wires) which cost extra but if I did it again I would just go for metal - I just think some people notice anyway cos they are observant and some people never even realise so it's not worth spending the extra money. Mostly I found people were really intrigued/wanted to do the same but felt it was too late. I was 41 when mine went on and 43 when they came off. I had to have elastic bands for about 6 months - a bit fiddly, but fine.
There was a bit of pain and irritation every time they were tightened and I did struggle to bite down in to things like apples of French bread. But no problems with staining - if you eat curry every day might be a problem, but the bands (which are the bit that can stain) were replaced every 6 weeks or so anyway.
Now I have a fixed retainer top and bottom at the front and retainers at night (there are like the invisalign trays) but after my next visit which will be one year post-removal I can drop the number of nights I wear them down. You teeth will move back if you don't comply, but one advantage of doing this as an adult is that you are presumably paying for it yourself and therefore are pretty motivated to comply. Mine were £3000 in total and most places do payment plans.
My ortho is a total perfectionist and the £3K has covered almost a year of after-care. I expect she might now see me once a year at the most. She was brilliant and I'm so pleased with the result. I think it's more and more common to see adults wearing them - I notice it all the time, but that might be confirmation bias!
Invisalign is always tempting but you really need to discuss with an ortho. My understanding they are fine for minor, cosmetic tweeks, but to properly move your teeth and keep them there you'll need braces. The older you are the more time it takes - your teeth will move quickly but it's training them to stay there that is the problem. As adults obviously your teeth get set in their ways.
Now I need to save up to get my whitened, but that's another story! Hope some of the above helps.