Pros
Duolingo is AMAZING for so many reasons! It was so easy to feel great and proud about the product... providing free language education for the world?! .. while you are learning languages on the job in a multicultural international team of really motivated, skilled people?! Yes! This helped for integrity, because language specialists or mentors interfaced with the community and did not need to hide any bad stuff. Duolingo is led by two co-founders who are ingenious, have an amazing intuition and impressive work ethic. They are open for feedback and have a sense of humor. Yes, there is room for improvement but that is self-understood, comes with being under 35 and leading such a start-up. As for training? There was a lot of on-the-job learning. Co-workers were open to teach you things and hackathons were great occasions to self-teach yourself things. But with about 40 employees, this company is just about to get big enough for formal training. Occasional programming classes were attempted. So this is a future need and something to ask for. Time-off policies, vacation days, flexibility, working remotely etc. No problem. They seemed to be very open to find solutions that work both for Duolingo and the employee's situation. No complaints, seriously. E.g. as a language expert, you gotta go home to freshen up your skills, so there was support. Compensation. Alright for language specialist. Probably better for designers and engineers, which is an overall issue in the industry.
Cons
No reliable formal training. Duolingo could benefit from formal training for employees with less skills. Targeted activities to improve office culture. While there were many fun activities that surely helped, Duolingo could benefit from some professionally guided interventions. E.g. on cross-cultural communication, working with remote teams etc. Not enough life for some people in the more demanding positions. But this is probably the case for all young start-ups. Employees were needed after hours, on weekends and quick at times.