That 'market' is called crime, and obviously criminals will be more than happy to fork over money for tools that help them to commit crimes without being arrested. In reality though, that market doesn't exist because if you or I would address that market we'd be hit hard by the authorities, and for good reason.
That said, having met the "ad tech" industry[2] when doing a search engine I can say there are a large number of people who are perfectly happy to take the money from bad actors with a "perfectly legal" product and reasonable deniability.
But all of these schemes have a certain "addressable market" and an "expected return" which are hard to judge. Putting numbers to the "completely anonymous" phone scam was interesting.
[1] https://www.wired.com/2012/11/zeta-radio/
[2] And to be clear, there are legitimate folks trying to do ad tech in legitimate ways, but there is also a lot of fraud in ad tech which involves setting up networks to take money from advertisers and feed it to bad actors.
I think this part is underestimated by most people. Celebrities are frequently under a microscope and having to live your life while worrying about somebody overhearing it and taking it to the press must be frustrating. Everyone has bad moments in their lives, but at least for most of us these won't be dragged up and published to the world. A device like this could help alleviate that fear a little bit.
They quickly found their primary market was, well... crime.