Pros
Three years wasn't a short time to invest your life working in a start-up company. I remember the first time I decided to join this company as a fresh graduate, I was someone who was still naive and had limited real-world working experience. But in a short time, I was able to get promoted to a senior position. I think it's confirmed that working in this company for 3 years is like working in another company for 4-6 years. You can compare my experience now with someone from another company with 4-6 years of experience. It's a good place to grow because you'll learn so much from hands-on experience and also from working alongside mentors and managers. It helped me get used to the pressure and rectify my time management skill.
Cons
Long working hours and heavy workloads, but well it is expected for a start-up. Also, they compensated you well with all the benefits. It's true that this company is not for everyone if you cannot handle the culture which is straightforward and very frank.