Status Updates From Postern of Fate (Tommy and ...

This reads more like a radio play than a novel. Almost everything is done as dialogue - including all of the exposition. There is very little description of places. The chapter headiings read like the title cards between scenes of a silet movie. This means that there is no authorial voice guiding the reader and no coherent point of view. It's a little like eavesdropping.

The humour works. The pace is a little slow.

I think Christie was having fun saying farewell to two favourite characters.
It's light, moves slowly and is mostly powered by humour.
The banter between Tommy and Tuppence has evolved from the lively but brittle exchanges they had in 'The Adversary' fifty years earlier, to gentle fencing in which Tuppence is clearly dominant.
Tuppence is still energetically curious. Tommy is pulled along in her wake,