Thermometers and blood pressure monitors are passive devices. Ultrasound systems do emit radiation, in the form of ultrasound vibrations from a transducer of some kind. In the ultrasound industry, there are two measurements, mechanical index (MI) and thermal index (TI) used to characterize the power being transmitted into human tissue. Clinical ultrasound manufacturers usually have a lab (AP&I "Acoustic Power and Intensity") to measure these parameters to stay within what are thought to be safe limits.

You can believe they are conning their users, but if you want to manufacturer and sell ultrasound systems, you generally have to comply with many different regulations.

If you actually read the FAQ on the website (https://www.butterflynetwork.com/pricing) you'll see that you don't need a license to continue using the product:

> Your Butterfly iQ will remain functional even without a subscription. You can continue to scan in all 19 applications, but will not be able to upload new images. You will have full access to all images in the cloud that were previously saved.