Metglass is a company that makes ferrites. It is not a particular kind of material. There are many companies that makes ferrites. Metglas ferrites of a particular kind (say, cobalt-based) are likely no better or worse than the same kind of ferrite made by another company.
Who made the glass in your car windows? Who made the ceramics in your breakfast bowl? Who made the plastic in the handles of your kitchen knives? Who made the ferrite in the cores of your motors?
Just like there are tons of companies making aluminum, steel, plastics, and other standard materials, the makers of objects generally don't disclose who supplies their materials. I wouldn't be able to look at a motor or inductor, and tell who made the ferrite in the core. Might be using Metglass ferrite, might be using TDK ferrite, might be using Micrometals ferrite, or one of a zillion other manufacturers.