I would like to know where the theory about corn providing more "heat" than a prepared blended food. A calorie is a calorie, no matter the source. As I understand it, fat content may play a role, as it is high in calories and usually slower to be digested, thus perhaps "staying in the system" longer. But, calorie for calorie, either feed or corn should provide a similar amount of "heat". I would love for someone to provide some actual documentation regarding the theory that "corn is superior for providing heat". From the reading I've done, fat content of corn closely matches that of layer pellets, and layer pellets often have corn as their main ingredient. So, let's see a study that supports the corn and winter heat statements.
As for Dumour compared to other brands, if Dumour is what the wallet will tolerate, then, Dumour is what the flock will eat. I readily switch back and forth between 2 local feed stores, buying which ever feed happens to be cheaper or fitting into my travel plans. I prefer the competing brand, but, my wallet makes the purchasing decisions, and my birds happily eat either brand. By far, the most important purchasing decision is driven by the mill date on the feed bag. If the feed is not fresh, I refuse to buy it, no matter who makes it.