But reading the accurate time in at least 24 time zones "at a glance" is hardly possible to fulfill the criteria of a proper worldtimer.
Stowa offered already in the 1950s such a map based time display, as did Christiaan van der Klaauw with his Mondial model. Adding longitude markings helped here, but since the time zone borders are politically established, knowing the longitudes does not yet lead to an accurate time reading.
Lottermann und Söhne in Germany therefore came up with a graphic solution based on a suitable map projection combined with detailed printing to make it possible to have a chance to read the different zone times "at a glance" from the dial.
Personally, I believe it to be a better solution to make the additional display a zone time one, as Bovet does it with the Dimier Recital 18 model. You can then use a decorative earth map giving an approximate clue about the time in other zones, but offering accurate time reading in one zone at a time. This is achieved with a marker (hand) connected to a reference city disk used as a setting help.

But together with the in-house movement, the Arnold & Son offering looks nevertheless attractive to me. So I will check it out at Baselworld.
Björn