Ok, here we go.
I have attended the Deva Curlaboration, a one day instructional for stylists where you pass for attending and cut a maniquin head. I was chosen after an extensive application process to train with Ouidad over two days on 12 models where Ouidad herself lectures and demonstrated the technique and personally oversees the ten people in the class/interview. Not everyone passes. I am uniquely qualified to explain both methods. I have been a stylist for 20+ years with curls as a focus and my clientele is 90% curly.
The Deva cut is done on dry hair with little or no product and is snipped one curl at a time without ever elevating the hair above 45 degrees (or paralell to the floor, for you lay people) it's a bit like pruning a hedge creating shape from the outside which has to be relatively the same because of the limitations of elevation which determine the amount of layering or shape. There are just certain haircuts you can't do without elevation. In my opinion Deva cuts all look the same.
The difference with the Deva and the Ouidad is this, while Deva is cut from the outside in, the Ouidad is from the inside out.
The hair is cut wet, (because the curls are never in the same place so dry cutting is sort of moot) the outside design line is cut depending on the haircut you want. Then the stylist uses the patented technique the "Carve & Slice". The stylist creates movement and incredible spirals by reading the curls in vertical sections, not horizontal and carefully makes a series of very delicate small carves and slices. This is never done to the scalp,( who would do that?) but at selected areas depending on the heaviness of the curl. The result is miraculous spirals, removal of the dred pyramid, incredible lift and movement. The comment I hear most when the ladies see the hair on the floor is "That's it?" This is not a massive culling hack up like thinning. It bears no resemblance to thinning at all. This increases movement and the life of your curls in a way you can't believe untill you see or experience it.
The reason you don't know very much about Ouidad if you haven't gotten a cut or talked to a certified stylist is this, there only a select amount of people who can pass the training and go on to become certified and you have to hunt them down. They are usually not around the corner unless you are in NYC or LA and the recipiants are happy with their hair and aren't complaining about their hair on the boards because it is great.
I know, one stylist, much less a certified stylist, may not change your mind and not everything is for everybody but if you haven't tried it you don't have enough information to have an opinion one way or the other. So if you want your hair to do something it isn't doing and no one has been able to solve the problem for you, I suggest you try a Ouidad Certified Stylist. The haircut last about 12-15 weeks or longer. I agree that Ouidad is opinionated about her method, why wouldn't she be? She thought enough of it to have it patented. If the Deva cut works for you get one, if a random cut makes your curls sing, stick with it but if nothing has worked to make you happy you haven't tried it all unless you have had a Ouidad Carve & Slice. Combined with the "Rake & Shake" application method of applying product you will have the most amazing curls you have ever seen. I see it every day.
If you have any questions feel free to contact me and I will do my best to answer them for you or guide you to someone who can. This are just my observations based on my experiences behind the chair. I am sure others have different opinions, I am not interested in debating so let me be clear, so there is no mistaking what I am saying. I prefer the Ouidad Cut, I think it is better than the Deva cut. If you have a Deva cut and like it I am happy for you because I want all curly girls to love their hair period. This post is speaking to people dissatisfied with their hair who want info on this method compared to another. I've done my best to explain it to the best of my ability.
Have a great hair day..