The plastic base must have been a cost cutting exercise. They were manufactured between 1977-Q1 (X1) and 1981-Q4 (b4).
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.
The date code was moved from underneath the base plate to inside the head as can be seen in the 4^th image below.

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