How did Microsoft's mixed reality evolved from hololens?

Hello, I found this article about microsoft's mixed reality. It says it is a new generation of VR, and it evolved from hololens that came out in 2015. I used hololens, so I am thinking to try mixed reality! What are advantages?

Best,

 

VR: Opaque HMD, cannot see real world. All observed content is digital.
AR: Semi-transparent HMD, can see the real world, supplemented with whatever digital content you want onto the visor.

I think the first thing someone needs to do is define Mixed Reality in a concise way before anyone can take it seriously. As is, the definition is unclear and it looks more like a buzzword than anything else.