The City of London is very small, safe (quick look online returns that the crime rate is "73% lower than London and 67% lower than national average"), and very rich, and obviously right in the middle of a top world city. So I am guessing that their police force is well resourced, able to attract "top talent", and not bogged down by anti-social and petty crime.

Well it’s a reputation, so it’s hard to quantify. But anecdotally I’ve heard from numerous people who had dealings with that they were very competent (compared to most British forces presumably).

I’ve also heard that their average level of policeman is more educated , ie many holding degrees, masters etc. I presume this must be due to the nature of the work they’re most known for ie combatting complex fraud, organised crime etc

Their focus is more on complex financial crimes, so they're a bit better educated than your typical cop.

They have different branding from the rest of the police forces!