I have to say, that I have only used the conventional undercut; and, it has served me well here in the northern end of the pacific northwest; even in standing dead Douglas Fir (up to 60 inches diameter) cut for firewood; on all types of ground and have never had any complaints. I guess it comes down to what you are taught and what your'e comfortable with; (and what the regulations require). I admit that I have had to add splint cuts (90 degrees to the horizontal cut of the notch) and a plunge cut in the center of the notch on some of the larger trees; however, if one takes care to construct a correctly formed undercut regardless of the type; and, makes sure to place the back cut the correct amount above the horizontal cut of the notch; and, leaves 1/10th of the diameter as a hinge; then, the tree always falls where you intended it to go.
( as long as you aim the positioning of the horizontal cut correctly) Also I was taught that the mark of a professional faller was that he/or she always had a large amount of
wedges with them and used them in the back cut. I have had three sets of double wedges (with sawdust in between the wedges ) in the back cut of a 65 inch diameter dead Fir I was felling for firewood and still had wedges left over. ( I know; I know; I can hear y'all hollering... wedges... huh... don't need them....) Oh; and that 65 inch diameter tree was on really difficult ground; and went down quite nicely I might add... though I have to admit it did end up landing about ten feet down slope of the front of the stump. I think what I am trying to say here is that you use the tools and experience you have; to assess the situation for each tree; and safely get the tree on the ground in a reasonable amount of time.