I just got the P323-A model. Zen-On also makes recorders alongside Aulos and Yamaha. The Zen-On brand of melodica is made by Seiko Instruments.
The upper half of the P323-A holds the mechanisms and the reeds, while the rear panel actually seals the reeds in. The moisture valve, mechanism-wise, has similarities with the Melodion, but there seems to be two buttons–one of them is the trigger, the other plugs the valve.
The sound leans towards being a harmonica, somewhat like a Melodion IMO. I will try taking pics later.