Even though I wear metal braces, some of our patients are doing the Invisalign treatment and they do work, although it's just for minor tooth movement. Compared to traditional braces, Invisalign is more comfortable, because you don't have the brackets and wires. But your teeth will still feel sore, because your teeth are moving.
As far as affordability is concerned, they are much more expensive than traditional braces. The company that makes Invisalign, is the only one that does these types of aligners (monopoly). Since there is no competition from anyone else, they charge a lot for Invisalign and they get away with it.
Personally, i see nothing wrong with wearing metal braces.
I work as an orthodontic assistant, and I wear braces too.