I've participated on their forum for years and a I've seen enough of the code to feel good about it
certainly more confident than the alternatives, and I know with certainty the voice assistant I'm running doesn't leave my home because I configured and verified it myself
Is it really open source? Do you really trust the entire operating system you are forced to use and not build yourself is what they say it is?
[0] https://www.home-assistant.io/installation/generic-x86-64