It sounds like they are trying to fly under the FDA thresholds for regulation as a medical device and be considered a low risk "wellness device" which makes no medical diagnostic claims and has low risk. This is why it is in spas and not doctor's offices.

https://www.fda.gov/regulatory-information/search-fda-guidan...

> FDA may consider certain products that use non-invasive sensing (e.g. optical sensing) to estimate, infer, or output physiologic parameters (e.g. blood pressure, oxygen saturation, blood glucose, heart rate variability) to be general wellness products when such outputs are intended solely for wellness uses, and provided they:

• are non-invasive and not-implanted;

• do not involve an intervention or technology that may pose a risk to the safety of users or other persons if specific regulatory controls are not applied;

• are not intended for the diagnosis, cure, mitigation, prevention, or treatment of a disease or condition;

• are not intended to substitute for an FDA-authorized, cleared, or approved device;

• do not include claims, functionality, or outputs that prompt or guide specific clinical action or medical management; and

• do not include values that mimic those used clinically unless validated (e.g. manufacturer testing, peer-reviewed clinical literature) to reflect those values