Pros
Prior to Jump, I spent time at various finance/tech companies in roles ranging from backend software engineer to portfolio management to trading quant research. The culture at Jump is by far the best, and if the circumstances are right (more on this below), I will return without hesitation. The company is extremely aggressive and demanding when it comes to business and growth, while staying patient and accommodating when it comes to nurturing people and talent. There are almost no places I can think of where you will learn as much in as short of a period time, with as much of a ramp-up time as you need to learn the ropes, while having almost unlimited financial and career upside to boot. I have personally seen one of the founders bend over backwards to accommodate an employee who had trouble fitting in with existing trading teams by naming that employee head of a new trading team; I have seen a team fail and reinvent itself multiple times while maintaining unwavering support from management to keep investing in people and technology; and I have seen people's careers absolutely skyrocket in just a few years after graduation from the amount of impact they are able to have from day one. This is a place where senior leadership wants you to succeed and grow the pie, and very importantly, where you will be recognized and rewarded for doing so.
Cons
I ultimately decided to leave because I wanted to take a chance and start my own company. While Jump can give you a point very far on the risk/reward curve, definitely far enough for most people, it can't quite provide the two-hackers-in-a-garage ride-or-die sort of deal that I (probably foolishly) wanted as a next step. Who knows--maybe I'll look back as a multi-billionaire and think that leaving was the best choice I could have made for myself. More likely, I'll come back as an older and wiser (and greyer) scholar of the markets, and with that entrepreneurial itch scratched, I'll ask for another chance.