Something that can have a huge calf, used him the second year he came out an had a train wreck on heifer's an mature cow's even had problems, and i heard all kinds of problems that year, the heifer calves come smaller but still had to pull it.
I never had any calving issues with him we used him on a second calf heifer with good results. She was a purebred simmi structurally sound, long bodied, and fairly deep with some decent shape. He really gave her added muscle and cleaned up the front end. I have a friend that uses him a lot and they don't seem to have much calving issues with him. He just always says not heifer safe. I think our calf was around 80 lbs.
I used him on a heatwave/angus first calf heifer. Ended up with a sweet black and white heifer. weighed about 65 lbs. We showed them as a pair at the world beef expo last year. champion commercial 4th overall.
The only thing I've ever heard about SOS is that they can get a little straight... I would use him on really sound cows with plenty of flex and cushion. I'm not sure exactly what he brings to the table that makes him a reason to use him. I'm a Simmie breeder, and I've never actually seen an SOS calf in these parts.