Yes, these are hinged transformers, so the cable does not have to be unscrewed and looped through.
I have the neutral conductor sensor in there just to see how much current is flowing in the three-phase network (3 phases),
and how much single-phase appliances (i.e. almost everything except heating, heat pump, cooker, etc. in the normal domestic grid) need.

Yes, the sensors are foldable and unfortunately quite bulky, and their cable is also quite short - but you can easily make an extension, even several metres are possible.
The fact that a sensor for N is mentioned makes no sense with 3-phase current and is, in my opinion, a documentation error.

yes, the current clamps can be opened for installation.
i think an additional current transformer on the neutral conductor would be ideal for detecting installation errors.