I'd never do it either, not because of privacy concerns but ethical reasons against Facebook benefitting from whatever they gather about such transactions.

To the other commenters, I'm sure the poster is aware of HIPAA. Luma Health works with Aptible, an "HIPAA Security and Compliance Platform". (Source: https://www.lumahealth.io/about-us/ near the bottom, and https://www.aptible.com/)