These Adjustable's are both the last of the "Adjustables Era" that started in the middle 1950's and also the last (until recently) Double Edged razors that Gillette produced.
They had already cut costs by making the base plate in a plastic and I guess that the Diamond knurling was cheaper to produce then their other knurling.
Its a Twist To Open, one piece razor. The handle is aluminium, the base plate plastic. The rest of the parts are Chrome plated brass.
They were produced between 1980-Q1 (A1) and 1988-Q2 (I2) when cartridges started to gain popularity. Remember that Gillette's philosophy was to sell blades, so selling cartridges made so much more sense.

How does it shave?
Its a mild to low medium shaver. At 109mm I personally find the handle too long.