The UI looks great! I like being able to easily visualize my applications without having to log into each individual node/container myself.
There are not many cons but it's been easy enough so far to figure out how everything works together once you get started using it. Haven't encountered any bugs yet that have caused me grief while working through them. We use this tool primarily within our DevOps team (our developers can build their own docker images from scratch or pull existing ones off helios) which has helped us keep track of all those builds we're doing throughout development cycles.