I don't think it's correct to stereotype all early flowering males into the hemp or non potent category. I have seen early flowering males that exhibit many of the traits that are listed in this thread as hints of potency. I have seen early flowering males with very hollow stems and produced tight flower clusters that smelled very strong on a stem rub. I've also made seeds with early males that produced plants that came out quite potent.
I have also found it to be that the males from the present generation often pass their traits to the female plants of the next generation. Tight nodes, branch length, smell, etc. Like somebody mentioned, it depends on what you are trying to accomplish.