Convinced my dad to buy a halfblood Simbrah bull back in 1983 (this was in east-central AL) - to run over our herd of Hereford/black baldy cows. NO calving problems, even out of heifers - and the resulting calves were the best we'd ever produced up to that time. I have no idea what Simmental or Brahman bloodlines were behind that bull, but calving ease was not an issue.
We've had Simmental influence in my herd ever since...but have always selected Simmental sires with CED at or above breed average, even for use on mature cows. Simmental breeders have done a great job over the last 30 years addressing frame size and calving ease issues. Most of our high% Angus cows are significantly larger than the high% Simmentals.
Current walking herd sire is a homo black/polled Simmental bull with CED of 14+...breeding all heifers and most of the cows, we've had only one that required pulling... probably an issue with the heifer and her pelvic size & birthweight behind her more so than the bull.
I'm a red cow man at heart and loved the original red Simmis, but I know that just because they're black, they're not just an Angus-cross - but I'm relegated to having to breed toward black hide to counter market discrimination.