Excellent interface: the docs are a little opaque in places but all in all one of the best implementations I've worked with. Their use of scoped keys (https://keen.io/docs/security/) to allow client-side data access is pretty awesome: very surprised that I haven't seen more usage of the technique in other data providers. The ability to provide client dashboards that directly access Keen's servers from within our web app without needing to proxy the data through us is simply awesome.