Custom dyno tunes from a reputable shop are always better then mail order as they're made specifically for your car and they'll give you max gains. But I wouldn't do a dyno tune until most of my performance mods are done so I don't have to go back and get another tune after I add like a cold air intake or something it'll just cost wayy to much.
Since you have not listed any mods, i will figure that you have none. First, the itsx is just a tool, you load your custom tune on it, then load it on the car. If you are planing on modding a little at a time, then go with a tuner that comes with ( Tunes for life). If you are doing a complete build, go to a tune shop. I do not care, to carry around a tuner, so I am custom tuned, and i am very happy with it. Been running the same tune for 3 years.