They will grow like a weed, top 1% WW and YW at 93% accuracy. I've never used a SimAngus bull that will out grow them. Use him on them cows are a tick slower on average for docility. United won't help with it. They are not man killers or anything. They just have an extra gear.
We bought a son of him at Hook's sale few years ago. Great bull, now got just couple daughters calving out of him the 2nd-3rd time. Really nice cows, haven't kept any direct daughters of United myself.