Carbon fiber can be extremely strong, stronger than steel in fact. However, I've also seen plenty of carbon fiber bicycle frames broken, and there's been some cracking of plastic on the CTX that some have attributed to the carbon fiber lower rod. It's MAIN advantage is weight for detecting, but it seems kind of a paltry savings when you're just talking the lower rod. I imagine maybe that Minelab was seeing some broken shafts by old fogies using their detector as a crutch to get back up....or else they thought by throwing the word "carbon fiber" in there it helps justify their price on the CTX!
Airplane manufacturers use a lot of carbon fiber for the bodies. They have certain rules about how old it can be / how many times in and out of the fridge. With carbon fiber, you work with the sheets while cold and then have to heat it to set it. Those competing in the solar car contests in college in a serious way use carbon fiber for the car bodies.
And yes, that's where my experience working with it comes from thanks to a large donation by Boeing.