Pros
1- Twitter NYC is still a small engineer office, you have the chance to know everyone and influence through mentoring and hard work (or used to be that place... more on that on cons) 2- The engineering team is a very diverse group, from cultural aspects, professional and academic backgrounds. It not only fits the image of NYC diversity but also makes it open to diversity. 3- In Twitter, you have the chance to work with open source at large scale. See Twitter's github page to have a perspective on how much contributions there have been made and the frameworks you'd be working on.
Cons
As a rational candidate, you can observe the high rate senior engineers and engineers managers departures have left the company after 3-4 years. If you are optimistic person, take the fact they are fully vested and keep the pros. Otherwise, read-on.. Since the IPO, eng managers are unable to push back upper management decisions. Frequently, because they are young first-time managers, they start acting erratically against their own team, including arbitrary job terminations (e.g.: engineers were recently promoted before being terminated under the excuse of underperforming). As result, they inadvertently create dysfunctional work environment, since people either get emotionally detached from work or fighting for survival (in a remote office it becomes even tougher b/c there is no place to go.) At IC level, if you've been in the industry long enough, you know what to expect from engineers in self-preservation, e.g.: code being pushed into private git repo's WHILE design review is still underway to get ahead of the "competition", obnoxious code reviews to slow down the "competitor", never questioning dysfunctional management decisions in meetings (playing the favoritism game.) Twitter was once a great place to work because it fostered creativity in engineers, giving the opportunity to grow their careers truly on a merits basis, i.e.: from own ideas to execution. Most of the work now is on-demand basis and most of self-expansion would happen during your extra time (yet not very valuable nevertheless.)