NotAnother - I have them in now for the second time. The first time was 10 years ago.
The good news is that Invisalign definitely works. You do need a retainer brace on afterwards - in my case, this wasn't applied to the back teeth and over the last decade some molars were beginning to move inward, which is why I'm having it again!
The problem with Invisalign is that it's not as invisible as you might think due to the attachments they apply to certain teeth to move them more effectively. These are like tiny concrete bumps moulded to the tooth surface. You won't need them on all the teeth obviously, it varies case to case. The brace is moulded to fit around these bumps so it can look and feel more bulky than if it was fitted flat.
Having said that, some people now have Invisalign without the attachments and it can still be very effective. I only have 2 this time and they are tooth-coloured and hardly visible at all. Last time there were more and I was more self-conscious about it.
They don't massively recommend Invisalign for teens as you do have to take it out every time you eat and drink, so teens on the go are likely to lose the brace or not wear it enough.
There is something called "6 month smile" which only straightens the front teeth.
Nowadays, you only have to wear each brace for one week. It used to be 2. So I have a 14 week schedule to perfect teeth! They send you a virtual image of the way your teeth will move from beginning to end so you can track progress.
My treatment this time is £2,500 but it varies according to how many braces will be needed.
You could also look into fixed lingual braces (behind the teeth), though this is often more expensive.
Good luck!