I've delayed writing a review for the CX-12 Jazz as I was a diatonic harmonica player who was new to playing the chromatic and wanted to have more experience before having my say. I feel I now have had enough experience so here goes.
1. Playability: Good but can be difficult in the higher registers. I thought originally this was down to my inexperience but on searching the internet have found that even experienced chromatic players have found the higher notes to be problematic.
2. Construction and Maintainability: Excellent. Well made and the CX12 must be the most maintainable harmonica on the planet. You can disassemble the harmonica in seconds and all the parts are available as spares.
3. Value for Money: Not good value if compared to the basic CX12. The Jazz has a different case and supposedly slightly higher reed offsets. People who are better players than me have said they can feel and hear no difference between the reed plates. I bought the Jazz as opposed to the normal CX12 as I thought, being a lip blocker, I would find thinner mouthpiece easier to become accustomed to. In retrospect I think this is not the case as even with the Jazz style mouthpiece I still had to learn a new embouchure. Having said this the mouthpiece is more the style and shape of a traditional chromatic, so if you already play a chromatic, or have other chromatics, the extra cost may be worth it,