Pluspunten
MongoDB is a highly reputable SaaS company and the C-suite knows what they are doing. You will learn a lot here. I can't speak highly enough of Dev Ittycheria the CEO, he is the real deal. Work culture is great, supporting a hybrid model (where remote work is allowed but in person is definitely encouraged in the hubs like HQ in NYC).
Minpunten
The Sales org runs the company, other business functions play second fiddle. Whiplash may arise when the sales leaders return from their annual offsite and present a new framework to the rest of the company. (but it's also a strength in that the Mongo sales team is probably in the top 5% tech sales cultures in the industry.) Where it can come into play is from a resourcing standpoint. Expect that if your team is not in Sales, you will run super lean. Secondly, as the company has become quite established (and big), many of the processes are fully built out. Depending on the org you are in, you may be more of an "operator" vs an "innovator". This comes down to personal preference on what you are looking for. But it definitely felt like a big company when I left, which wasn't the case when I joined.