Microsoft also have a camera passthrough, which provides the "mixed" reality.
At the same time it announced the rebranding, Microsoft also confirmed it will bring mixed reality to Xbox One, as well as its next-gen Project Scorpio console (yet to get an official name) that's due to arrive towards the end of 2017. Now, it's not yet clear whether this will include all of the mixed reality headsets like Acer's, some, or new, specific headsets. Right now the message is a tad unclear, but we'll likely find out more at E3 2017.
By now you should know that Sony has its own virtual reality headset for the PS4 called PSVR. The headset has been on the market for a few months now, and sales are good at almost one million in four months. However it's purely VR, which is why Microsoft may have an edge with its "mixed reality" angle, assuming it turns out to be a compelling user experience.
So Microsoft's proposition for a console headset has the potential to be quite different to its rivals. Let's hope it delivers.