I believe it to be a product of "Prototype Putters", a seller on Ebay who has a source that seems to feed him odds and ends that all look to be OEM over-runs or "open models" from foundries outside of the USA.
He has some that he sells as handmades and I have no idea as to those pieces. This one does not look to be hand milled, but more likely cast with a skim milled face. The texture in the cavity and remnants of that same texture on the shoulders are telling that story.
Just my thoughts and if you like the putter, the story should not make or break the way she rolls the rock.
Best of luck,
LaMont in AZ