Pros
The R&D team has some of the best and brightest engineers you'll have the pleasure of working with. Whether you consider yourself a software engineer, data engineer, data scientist, or devops engineer, there are large, exciting, and challenging problems to keep you engaged and continually learning. This is a fantastic place to get your hands dirty with cutting edge technologies, and you'll be doing it alongside dedicated, hard-working peers and a resourceful product team.
The R&D team is also a strong believer in career growth, and facilitates opportunities for continual education (e.g., conferences), knowledge sharing (e.g., lunch presentations by resident experts), and personal growth goals (e.g., leadership training).
All the exciting work is supplemented by great benefits that include a gorgeous and convenient office, catered lunch, a fully stocked bar, regular happy hours and off-site activities, unlimited vacation, great healthcare, commuter discounts, etc.
Overall, there is a great foundation to improve upon for builders, and plenty of green field work for designers. And you won't easily find a better work environment than this.
Cons
The transition from small to mid-size company can be painful. The breakaway from bootstrapped teams, tools, and processes towards a more scalable, robust organization is taking time and has been jarring for some. Bridging the culture divide between R&D and sales/marketing takes energy that many don't have.
Unsurprisingly, there are also too many cool things to build and not enough time to build them in.