I believe this to be a First Generation Erfa Rasant, this is according to a German Forum.

The handle, the bottom plate and the middle plate feel light, so I assume Aluminium. The TopCap is Zamak and the Twist Knob seems to me metal, so I assume a Stainless Steel of sorts.
Its a two piece and the twist knob is most likely held in by the adjustment indicator.

It's continually" adjustable - so has no notches. The dial is not numbered. It has   Λ   O   +   ×  as the symbols.

How does it shave?
I generally use it about ¾ of a turn open and it gives a pretty easy BBS with a little bit of blade feel.