I'm in possession of Linotype Typewriter 300 series. Is this worth any money? 

Where are you located? I would suggest to ask the nearest printing museum directly. 

Chicago area, thanks for the feedback

 

Typewriter –> Typeview

It probably only makes sense in a (well maintained) series 300 environment. Note that CRT monitors usually have a limited lifetime.

The system used to look like this:

Operators working on screens like this usually sat in an almost dark environment, thus avoiding frequent tiring adaptation from surrounding light in the room and the dark monitor. This also partially avoided irritating reflections on the screen of lights of any kind in the room. Trade unions and work councils (Betriebsrat) made a big issue of this. I recall operators and programmers getting a medical prescription for greenish tinted ‘computer glasses’. 

Funny enough many students nowadays prefer Dark Mode on highly reflective iPads while sitting in fully lit rooms …

Linotype Certronic 300

Input device (frontend; CRTronic) Disadvantages: not graphic-capable; no enlargement; character matrix and number of characters specified; reduced ASCii code so, for example, no German special characters can be displayed.

Typeview 300

Early backend; capable of graphics; several grayscales; DIN A4; full page can be displayed; page layout can be checked before setting on film (backEnd); for the time a high-resolution screen. It was the beginning of WYSIWYG