You know, I've been wondering the same thing. I'm curious to read some replies. I do know that once that Frontosa is big enough to eat an angel, THEY WILL. I am tempting to try it myself, but I'd keep a REAL CLOSE eye on them. Angelfish sleep at night on the bottom of the tank, and Frontosa's HUNT at night.
My Frontosa's would eat all the baby Malawi's at night when they were in the African Cichlid tank. And they (the Frontosa's) were pretty small themselves then.