The rapid maturing of the ISA Brown compared to the Orpington should make for an interesting young flock.
I enjoyed having Buff Orpingtons. If there are chicken breeds almost immune to getting in trouble, that is one of them. Orpingtons are too heavy to fly over most any fence. Usually, fairly lazy but they are peaceful and make good mothers and lay, kinda okay.
The ISA Brown are supposed to be one of those pre-eminent hybrid Sex-Links. There are likely ancestral lines closely controlled by some hatchery. Grandparent hybrids before hybrid ISA chicks.
I used to imagine that it would be fun to have both meat and laying breeds of hens with the appropriate roosters for sex-linked hybrids. Chicks could be sold with confidence as to sex. Not wanting the roosters around pretty much eliminated the possibility of me doing it, however.