I've recently completed the invisalign treatment, so I'm wearing the retainers now.
My dentist recommended the aligners to prevent gingivitis and to improve the health of my gums (I had "pockets"). The desired results were achieved - my teeth are straighter and it took approximately 17 months.
I do recall experiencing pain at the begining of treatment, but after the 2nd month I was used to it. However, I must mention one other added benefit to wearing the aligners - I lost weight!!! Because of the oral hygiene maintenance associated with wearing the aligners, I stopped eating as much as I was before and I also stopped eating certain foods and drinking colored beverages. I went from a size 12-14 to an 8-10 - which I did not expect.