different straighteners have different technology and different ways of protecting the hair. you also need to use a product to protect the hair. i use 2 different irons at work. for my curlies that want to go straight i use an iron from ghb which is ceramic and tourmoline. i am still learning about this iron, but it gets up to 374 degrees which is the heat in which even the most damaged hair can be straightened by this iron even though i don't suggest flat ironing dry brittle hair. It is suggested for even the curliest hair and gets it straight in one pass.
for my straight or wavy girls i use my chi iron which does a really good job, but sometimes i find it it get a little too hot for what i am doing.
i have also tried a ceramic iron called a super****(star) that i bought through a distributor, wasn't all the impressed on my curlies that wanted to be straight.