I have gotten the Matrix OptiSmooth treatment twice, and I was happy with the results both times.  My hair is naturally wavy-curly, and has a very fine texture.  It doesn't make my hair very straight, it just relaxes a lot of the curl and wave in my hair and makes it more managable and easier to style.  I also have color-treated hair, so my stylist uses the formula made for hair that is chemically-treated.  My hair didn't get any noticeable damage, but I do like to get a trim after the process.  It's pretty much guaranteed that your ends will at least get a little damaged since it is a chemical treatment.  It's possible it will make your hair straighter than it made mine, it all depends on the texture of your hair and how it reacts to the chemicals. 

Good luck!