Not everyone can build their own backtesting tool. I played around with quantopian for a little while and did some live trading with quantopian + robinhood and I never would have been able to do that without quantopian
I am not a developer, but using my brokers API, examples and python, it took me few months to build a very robust and automatic trading system... I did learn python by back testing my trading ideas... To use Quantopian you still have to learn python, so I am not sure where is the benefit, considering all the problems mentioned here...
