I was apparently a perfect candidate for this treatment, and the cost was the same as it would be with traditional braces. I have a big gap in my upper front teeth, the rest on top are pretty straight, just a slight overbite. My bottom front teeth are slightly overcrowded and slightly overlapping. I mention my condition because I think it's important to know that your condition is right for the treatment, or it will probably not work out well for you. I stress that you should get 2 or 3 different opinions if your condition is not 'slight', as I describe mine, or if you have any doubts.
As far as the treatment itself, it took me a day to get used to having plastic trays in my mouth when I first got them, but now, 4 weeks later, I'm completely used to it. I keep them clean by brushing them with toothbrush and toothpaste (gel cos its non abrasive) when I brush my teeth (after eating, before and after bed).
My breath is fine, I don't speak too funny (well, sometimes but its no big deal). I love that nobody notices I'm wearing them at all and that when wearing them, my gap actually looks smaller. My treatment is for 8 months. The Dr said by 3 months my gap will be gone. Can't wait! cos my wedding anniversary is 4 months away and I want a gapless smile by then! I'll be posting before and after photos when I get them. Good luck with whatever treatment you choose.