@badlogic It's not the most efficient protocol and consequently power draw is a bit higher than alternatives, but probably not enough to make a difference.
A self-hosted server can be rigged to not federate, though last I checked it took some doing. Privacy-wise I was most excited for the Matrix p2p project.
Re: "Might do my own client": In case of relevance, I recently published a first stab of a .net implementation of the client-server protocol (MIT): https://gitlab.com/framebunker/matrix