I don't have enough experience with Guinness females to say much as I've only had experience with one. I bought a cow/calf pair and that heifer calf at side was a Guinness. I really liked her phenotype and she grew into a real nice heifer. Even had her on the show string. Disposition was good. She was deep, easy fleshing and moderate just like I like them. Spring time came around and I snyched all the heifers up to AI. Thought I stuck her first round. Fast forward to July and getting set up to preg check. I saw her getting ridden by another heifer. Sure enough she was open. She didn't settle AI and didn't settle being with the bull for 90 days so she's getting fattened up to butcher here in the next month.
I did AI some heifers and cows for a neighbor of mine to Guinness because he liked the heifer I had so much.
That's about all I can tell you, I'm sure there's other people who have much more experience with him. I wouldn't be afraid to use him again as I can't place all the blame for that heifer not breeding on the sire.