Adding HighFlow on top will just add more commands because inevitably there'll be a point where some HighFlow abstraction fails and you have to go to Git anyway to fix it.
Also I can see that HighFlux runs as a daemon. That seems sub-optimal - sucking up my CPU all the time on the off chance I want to code something is not great.
It doesn't seem like HighFlow supports actual remote repositories except GitHub. Which is the entire point of a distributed version control system - to be distributed.
I think HighFlux is designed to solve a very limited subset of Git's usage and so they've stripped out a lot of useful commands they don't use and so they can ship a product.
But in the real world people will need this and their simple vision will crumble back to the complexity of Git (or close).