Jim Simons himself has engaged in some impressive philanthropy, but one perhaps should weigh that against the effects of the money spent by Robert Mercer, the co-CEO he left the company to (Zuckerman discusses Mercer in detail). Mercer and his daughter have a lot of responsibility for some of the most destructive recent attacks on US democracy (e.g. Breitbart and the Cambridge Analytica 2016 election story). In the historical evaluation of whether the world would have been better off with or without RenTech, the fact that RenTech money may have been a determining factor in bringing Trump and those around him to power is going to weigh heavily on one side. https://www.math.columbia.edu/~woit/wordpress/?p=11455