We used this in production at my previous role and it was fantastic. There are a few rough edges but it became markedly more reliable over the 2 years or so we used it. It handled huge (well over 100KB) queries generated by SQLAlchemy with ease and was lightening fast.

We were using it as part of a custom BI tool for portfolio risk analysis. The data was mastered in postgresql and loaded into MonetDB for OLAP stuff.

The developers are pretty responsive to questions and bug reports.