As seen from the Feather main page, there are two versions - Silver and Gold, this is the latter. Its numbered 900-1. With its Gold/Black colours it really is a great looking razor. I'm not sure why they didn't make the indicator dial also gold in colour.
I've been told that these come from the late 1950's / early 1960's. I have not been able to confirm this but if true, they pre-date the Schick Krona by about 5 years.

I'm not really sure that this should be called an adjustable as there is no separate adjustment plate and all the adjuster dial does is move the doors up and then open them. There are however five very definite stops.
They are labled as follows:
O - Opens the razor so that a blade can be inserted.
R - It opens the doors enough to rinse the razor out
1 - Most aggressive setting
2 - Middle Setting
3 - Mildest Setting

(Click on the case insert and instructions image below to open in a new window)