The tone is rich and powerful, and the response is very fast. People that have played them seem to like it. One has to remember that the inexpensive Italian and German concertinas were built for a particular segment of the market. The Herrington concertina is in a completely different class. One thing that caught my eye was that you use delrin buttons.
Plastic is a broad catch-all word, that describes a lot of different products.
It was coined back when the plastics industry was in its infancy. Today there are some excellent polymers that are very suitable for machining and make excellent concertina buttons. Delrin is such a polymer. It is tough, durable, machines well, and takes a nice shine. It is well suited to my design and helps me control cost.