I was a big fan LSF though I too remember him more as the 'second' centre-back, if you will.
He was resolute, could pass effectively rather than spectacularly, strong in the tackle and a real leader. If I remember correctly Furphy bought him? I'm not much for record books and my memories are fading in my advancing years. I saw his debut in the Watney (ugh!) Cup final at Bristol.
He was captain by the time the impossibly handsome Jimmy Sirrell became manager and played pretty much all his Blades career in a declining team.
I see what you mean about the K-Mac comparison and there are similarities but I'd see McDonald as a significantly more creative player. Keith Eddy did have an eye for a goal though. I remember we won 3-2 on match of the Day from 2-0 down. Was it Chelsea? Anyway Keith scored a good 'un. Maybe the winner if I recall correctly?
He was our third best ever signing from Watford! Sounds like faint praise but the two ahead of him are Currie and Agana.
I think he'd make my top 25 Blades list, if I had one!