Pros
Stability, prestige, it's a "nice" place to work. You get free snacks and coffee.
Cons
Endless streams of soul-destroyingly tedious work. Work that could easily be automated if the proprietary systems you'll have to rely on didn't... I guess the only way to say it is completely suck. Almost nothing you'll learn will apply in any other environment. The platforms and practices are so eclectic to Bloomberg that if you try and take them anywhere else, you're not going to know what you're doing. Things like career development, ideas like advancement simply don't exist there. You will be dumped into a massive pool of coders and basically just bang away at a keyboard until one day, you die. I weep for the torrents of inbound kids, fresh from school, looking to start a career and what they have in store for them. Bloomberg, the world is bigger than you. There are ways of doing things so foreign, so superior to yours that surely they appear to be some form of dark magic, and I understand your fear but if you push through it a little bit, you might be capable of amazing things. I quit, good luck.