I will say, since this thread I've used my Mixteca pot directly on the flame twice with no diffuser, and while I'm still anxious about the way it's a little wobbly on the grate, I've been astonished at how much faster the beans come to a boil. With the diffuser, I did often have the feeling that the beans took a weirdly long time to cook. I was definitely cautious with the heat, though, probably letting it stay on low for longer than necessary.
Also, for what it's worth -- I did a long-form cure of the pot when I first got it. I appreciate that Rancho has reported that it's not necessary with this pot, and I'm not trying to argue with anyone on the meaning or the science; but for whatever it's worth, that clay on mines was *dry*.