Speaking the truth. If one got a source of verified real Alpha you will have all the money you need. If someone say they got Alpha/edge but got no money they are either lying, a fool or have mistaken themself.
Personally I compare absolute eq return of underlying instrument to the absolute eq return of the trading activity in the same instrument for my selected time period. I do like to isolate the alpha component and plot it.
Not a perfect science: Use the Barclay's or JPM's benchmarks - subscription is not cheap. Use an established public benchmark. Adjust for leverage, but most of all have the PM explain what they're doing to gain Alpha. Factor in transaction costs which hurts vs. public benchmarks. Eyeball the trading history, again to see if the PM can justify their trading. Last year ESG managers had phenomenal returns and IMHO will underperform this year as 2021 created the benchmark. Some categories - like vol. books - are murder to quantify.
I think you're better off trading these "ideas" yourself. Unless you just walked out of a large hedge-fund (in which case you'd still be bound by an nda) or have other super credentials from the industry) your chances are almost 0. You will simply not be able to get through the door. Ideas in that world are a dime-a-dozen and who they come from is more important than what they are. FWIW, I have over 25 yrs experience in buy and sell side. Good luck