All instruments have hardened springsteel reeds. Every reed is mounted in a single brass frame and finally tuned by hand. The concertinas come with solid cases. One of the most difficult things for me is to describe the tone of a concertina and the difference in tone between the models and materials used. It is a fact that metal ends sound harsher, they have more overtones and are louder.
Wooden ends are softer, more mellow.
With solid wood there is the risk that it might crack, but up to now I haven't heard of someone having problems with that. The harder the wood the higher the potential risk of cracking. On the other hand the harder the wood the better is the sound. The hardest wood I use is ebony. Wooden ends are a bit lighter than metal ends.