Thanks so much for the photos. So what I think I see there is that the sound actually comes out through the keys in similar fashion to most melodicas. It is hard to tell, but the reed plate is covered, so the sound does not appear to be coming out the back of the melodica. The air comes into and pressurizes the reed plate chamber. When a key is pressed, the key valve on the other side of the reed plate opens. The air (starting in the reed plate chamber) flows around the reed, and the air and sound flow under the reed and through the open valve, exiting on the back side of the reed plate (up through the keys). This explains why there is no big sound difference when you tape up the holes.
I think that is how it works. Someone please correct me if I am wrong.
It does look like a nice instrument, and I am sure I will enjoy playing it. Every melodica has its own sound and can be used for certain applications.