Pros
I worked at Optiver many years ago, so take everything with a grain of salt. From a trader perspective, they do a lot right. The people are very talented, the software is cutting edge and fast, and the compensation/benefits are very good. I think they also did a good job creating and keeping a culture where everyone tries to improve, and everyone feels like they're on the same team.
Cons
I feel like the top traders don't necessarily make for the top managers, and they need to continue to train traders throughout their career. Non-traders sometimes were treated like second class citizens, which obviously shouldn't be the case. The culture is very aggressive - there's a ton of pressure to keep improving or you could be out of the company sooner rather than later, which is a lot of stress to have. And the comp structure, while good, was very top heavy.