I have an F75 that I have been using for the past 3 years and, you are correct, it is not fond of iron. You have to be careful with a good target reading being influenced by a nearby piece of iron. I always make a quick sweep around a target to make sure this is not the case. Also, I have dug some really deep targets that showed to be good targets at a shallow depth, but, were, in fact, deeper targets of large iron. The nice thing about the CTX is its' ability to track more than one target simultaneously and give you a better idea of what you are looking at.
I'm still learning the CTX (the F75 was very easy to learn in comparison), so, I have a ways to go. I feel confident that with more practice and the help of the good folks on this forum, that I will learn the CTX's language and be well on my way to finding more than with the F75.