Pros
I was one of the original developers of video ad serving product. The team (product/engineering) was able to identify an MVP product, and given enough time to develop a solid technical foundation. We had senior people with the right specific skills to build it (mostly) right the first time. The CTO was able to judiciously jump in and suggest fixes for my technical blind spots (unit testing), which made me a better developer. As the product became successful, we were able to proceed without major issues and mostly keep a good velocity of new major features. I sensed that junior frontend developers (mostly) had enough pre-existing standards to build good code and learn.
Cons
There were management and technical misses of course - the intern that didn't get enough guidance, some minor hacks that became impossible to remove without major refactors, but in general it was good. In retrospect, another miss was that developers were perhaps too siloed - I would have liked to spend significant time in another area of development.