Deva cuts didn't work in my case as my hair (3b) is coarse but is not dense, so after each of these cuts my hair looked short and cropped in the crown with strings of hair hanging at the bottom. I had three of them (with "very good" stylists according to the reviews posted in its site) but I wasn't pleased with any of them.
Also, it's true that you'll need to wear your hair curly all the time as your hair will look uneven if you straighten it.
However I want to give Deva cuts a last chance. I'm letting my hair grow very long and then I'm planning to go to Devachan (we'll make it a weekend trip to NY!) later this year and have my hair cut by one of the best stylists there. I'm curious to see if I get different results with longer hair and a real good stylist. We'll see!