My observation is consistent with NDM4 being more prone to splitting, but it seems to affect the early crop to a much greater degree. The NDM4 seems to poop out the first crop super early, and 90% of them split. The summer crop seems to fare better.
Dr Campbell also said that there was a failed non-#4 NDM planting in Homestead. The owners yanked the orchard due to lack of production. However, non-#4 NDM the trees in my housing tract (4 of them) all produce heavy crops year after year. The major difference is that the #4 is way more precocious. There must be some sort of soil issue going on. Homestead has really poopy soil (if you can call solid limestone rock soil). Here in Broward we have ghetto soil too, but it's quite a bit better than Homestead soil.
In taste and fruit size they are indistinguishable to me. A regular NDM tree grows more quickly than NDM #4 and the #4 seems to set more fruit. NDM #4 seems to be more prone to fruit splitting and I've seen conjectures like too much fertilizer nitrogen, soil conditions and variable water availability while maturing fruit to explain this.
I have had people tell me that they can tell the difference between them, but I certainly can't. To me they taste like the same fruit also.
And on the #4 splitting more than the original NDM...this has been my observation as well. Richard Campbell swears otherwise.