The way I would look at it at the moment is that it provides a nice self-service interface allowing you give people access to deploy containers on dev servers which may free up time to allow you to concentrate on managing production.

This. I evaluated Portainer recently and found myself missing a few critical features available from Marathon.

Such as? Let us know what we are missing, and we can look at adding it.. remember tho, we are not trying to be a replacement for Swarm, we believe swarm service orchestration to be a winner, so are supporting that (as opposed to rancher, kuber etc who have their own cluster solution).