I would argue that the golden age of hand-held light meters would be around 1947 to 1965--at least in the USA. Photoelectric light meters only became commercially available in 1932 (also by Weston), and during the Depression they were expensive luxuries--the sort of thing only professionals could justify. Then World War II. But after the war, and certainly after the manufacturers were able retool back to civilian production, prices dropped and new products were introduced. And a whole new generation of photographers were buying cameras, film and accessories. And color, of course. Color needed more accurate exposure than B&W.

After 1965, on-camera light meters had become so common that the average photographer didn't need a hand-held anymore. While many kept their old ones as insurance, it certainly didn't do anything to spark new sales.

The Master II came out right after the war, after the depression, when people had money and wanted to spend it. The Master was an excellent meter, very nicely finished, highly regarded, and well-advertised by Weston. And it didn't hurt that field photographers like Ansel Adams wrote about them in their books or were photographed holding them in their hands.

The Master II seems like the iconic one to me; I see it so often for sale, usually at inflated prices because most of them are dead now and the cells can't be replaced. It was also still from the era when it was calibrated for Weston numbers, not ASA, so the modern user needs to make allowances.

If you want to see what this looks like inside, check out the autopsy.