No, 100 dB SPL is not a fundamental law of physics, but it's certainly a fundamental limit of human tolerance (it's about the same sound pressure as standing next to an operating jackhammer), and even if you can't hear it at ~20 kHz, any small animal in the vicinity will likely be tortured (seriously, PETA should take an interest in this technology). And since we're talking about investing in a consumer technology, any fundamental limit in human tolerance or even FDA guidance should be a deal breaker from a business perspective. My objection is that no one did such a sanity check before investing a large sum into this concept.