We are all superstitious its inherent to us as human beings, even if it is not Fengshui like shamanism or any religion they will always connect something into it to have good luck and be guided in a path of uncertainty, but Fengshui is not only about superstitious like what I've been saying it has something to do with harmonious and clear thinking, I do believe in Fengshui but I am not a serious practitioner but I notice people who seriously practice Fengshui are happy, clean people and very meticulous on how they place things and check up dates for their activity.
I agree, maybe we can compare it to mantra I guess? but all in all if they want to believe in Fengshui then let us believe in that, because I don't know why it is kinda effective or maybe because just like what you said, it gives them clear mind that will help them to decide and come up with strategies, people who believe in this are more discipline than to those who aren't just my observations no offense to those non believers.
I think it will be different from a mantra because a mantra is writing that is said before they do something. At the same time, fengshui is a description or information obtained after calculating the formulation and then arranging what is needed. We are not clear on what and how Fengshui is because we are not practitioners, so maybe those who continue to use it feel comfortable in their lives. Maybe someday we can find out more about this Fengshui to understand it better than now.