I did a little digging and the mirrors I was trying to remember are Chuck Harris mirrors, which achieved an excellent reputation for durability, sturdiness and adjustability of the attaching wire, and design. He built them out of recycled materials and each one was unique.
Unfortunately Chuck Harris died last year at age 76 so those are not available. A big fan of his mirrors claims that a worthy successor is the HubBub mirror. Here is a link:
HubBub MirrorsI'm planning to order one, since I missed a good chance to get one made by Chuck Harris a few years ago.
Advantages of helmet-mounted mirror (IMO): I can move my head a little bit to see things in the mirror easier than bending down or stretching to see in a bar-end mirror; also I'm more comfortable presenting a narrower profile in many cases. A couple days ago found a truck parked right in my way, lots of hurried traffic on a narrow street, but just room between the truck and curb to ride through, carefully.