The use of something like this is that they require essentially no maintenance compared to something like a turbine, and should be significantly easier to manufacture as well. This could in theory make it useful for something like an off grid power generator, but the real kicker would be something like a moon base. It allows using thermal storage to store energy rather than batteries, which is significantly cheaper and can be built on site with local materials which massively saves on launch mass.

As stated there is also a military application. Since they run so quietly they are suitable to make power (to run systems, not thrust) on submarines, especially nuclear subs, which want to be as quiet as possible. I think subs already actually use stirling generators but this design is potentially quieter and more reliable.

Feels like reading about the "turbo encabulator". Also converting sound into electrical energy isn't the first thing that comes to mind to drive an ultra silent submarine.

Surprisingly it is still plausible. It is a niche application for a very specific form factor and purpose.