There is no reason that your dad can't take both ('one and 'ol). I am 40 and take 1200mg of CoQ10 daily. No health problems.
I don't doubt taking high amounts of each form of CoQ10 has no negative health implications. I take 100mg ubiquinol everyday myself. For people like me and you, we can do it. However for my Dad, he wants benefits without sacrificing anything. He finds taking supplements very inconvenient to the point that he moans it's torturing him, which is one of the reasons he is giving up. I have already tried to make the protocol as simple and as convenient as possible. Putting ubiquinione in coconut oil and heating is beyond his tolerance.
He stopped the diet too as he loves biscuits, rice, bread and carbs. He finds the diet 'torturous' as well.