The biggest problem with crossbred or composite bulls is they sire 2 or more sets of calves. By that I mean an Angus/Simm will sire some Angus type calves and some Simm type calves.
The odds are reduced somewhat if the cows are the same composite, but then they can throw 3 types, 1/4 simm type, 1/4 angus type and 1/2 angus/simm cross types.
Using Angus/Hereford bulls, they seem to either throw Black calves (so just use an Angus bull) or they throw Hereford looking calves, some which are black with the featherneck.
Using composites actually loses your hybrid boost in many instances.
Another factor involved is that composite bulls are often from the poorer cows of a breed that can't compete in a purebred situation. I have seen Angus cows that wouldn't raise a 600 pound Angus calf, but the owner has a market for those crossbred bulls so he breeds her Simmental. The calf weans at over 700 and sells for good money. The buyer never went back, he got lots of little calves and a few big Simmental type calves.