Other than everything emt said, the best feature with Pi is the Admin position window. Finally I can see my real buy/sell price and my actual P&L and not just MTM.
I don't know how many times I have squared off positions on NEST thinking I am in a profit, when actually I was not. Also the Admin position is auto refresh, so real time update of P&L, no need to click get positions every time.
But..
I am used to bracket orders now. Waiting for that on Pi to completely switch over from NEST.