>As part of that stack, we chose MongoDB + Mongoose ORM because the combination presented least overhead and allowed us to ship quality features quickly. As Sir Tony Hoare states, “premature optimization is the root of all evil,” and there was certainly no need for further optimization at the time.

Looks like the tool did a great job while they were getting started. Mongo is very easy to hack something together with, later on it looks like they just needed to migrate to something more stable