In Simons book it is also clear the main trading idea until today was brought from an employee of Morgan Stanley where they had some very good years until it stopped working for them then they got hired from Simons. There they could not make it to work because of transaction costs. At that time also Simons and his employees were looking for intraday seasonalities on the 5min timeframe, which is just bullshit, as there is no such fine seasonality to be found. I can admit this because I have it backtested too some years ago. It is just pure overoptimisation and curve fitting and nothing else. So the main edge was brought by his additional employees also from IBM for very good programmers to minimize transaction costs. That is their main advantage or edge. It is minimizing market impact when they enter and exit a position based on the strategy from Morgan Stanley trader. I also could easily imagine that those programmers who were than alone in their group with no very good traders that they did not look around on other similar very good strategies. So it is just the simple and pure strategy brought from one trader who was in the Morgan Stanley group and then also got fired by Simons in just a few years. His other employees were no traders just pure programmers, but one of the very best ones in their subject. So all in all it is about level2 and orderbook data and optimization to minimize transaction cost. That is their advantage I would say, of course with the basic strategy behind. There might be some variations with that brought strategy from one trader, but I am guessing they did not play with other strategies surrounding the original one too much, because the other employees were just programmers and no traders. Until today they only hired Phds in hard subject and not mainly excellent traders with new strategy ideas. That might be also a reason why their AUM is capped at $10 billion for many years now, as they cannot trade bigger size without harming performance too much (with that one finetuned strategy 'only').