How often do you get keratin treatments?

[Misshairdiva]

I'm still confused about keratin treatments. This may sound like a stupid question but what's the difference between a keratin treatment and a relaxer? Don't both leave your hair straight? If I were to get a keratin treatment how often would I get my roots touched up? Can I rollerset with a keratin treatment?

 

[BeautyBlvd]

I got one 3 days ago and the one before that was in April, this year I plan on doing it every 6 months. I know people that get a new keratin every 3 months, but I don't need that.