The 'bell' doesn't ring because there isn't anybody whacking it with a hammer. This shape is particularly resistant to mechanical vibration, and requires no bracing because there is no rear chamber behind it which could serve as a source of frequencies that could vibrate the structure. This rig is functionally identical to a small horn-loaded tweeter, just a lot bigger.Your concern falls into the same category as the persistent myth about metallic radiating surfaces, cone or dome or whatever, having a 'metallic' sound. They don't, because again they aren't being struck with anything, they are simply moving back and forth as pistons.
I haven't heard these but they do look nice.