We use mongodb for the analytics as well yes. It's a less obvious choice there than for the CMS part, but it's a good enough fit, in-place updates can be really

We use mongodb for the analytics as well yes. It's a less obvious choice there than for the CMS part, but it's a good enough fit, in-place updates can be really handy and we prefer not having 2 different databases. We don't index custom fields and for queries where that would be required we do the actual querying with ElasticSearch, but for simple filters on a custom field or the like, Mongo does fine.