The ML seems to scan rooms better and "lock" things in space better but the HL seemed to have a better resolution (_not_ field of view) when using "normal" apps.
They are both competing on field of view now with the next generation of devices but the ML beats the first gen HL hands down on the larger FOV.
Nothing else took its place, and, while still being popular, it quickly faded from the status of global phenomenon.
It's a nice money making game, but not a hardware seller.