Skepticism is certainly warranted based solely on the timeline presented and my experience in medical devices.
As to the rest, you're operating on incomplete information. According to the NSPE, "Engineers may express publicly technical opinions that are founded upon knowledge of the facts and competence in the subject matter." You say, "what should we do as engineers", so I'll make the implicit assumption that you're an unlicensed "software engineer" like many on HN. If so, consider that you may be operating outside your area of expertise without complete knowledge of the device. I would make careful public statements: I, for example, wouldn't say "I performed a first-principles analysis and, as an engineer, I find the device claims are impossible."