Did they have any curiosity about how it works?
I say something like “it contains messages and questions that stimulate your mind to create beneficial changes. You can’t hear them consciously, but they’re in there.”. Something like that.
I think that’s the minimum that they have the right to know.
On the other hand, some people just trust you and have no desire to learn more about it. Still, I’d say something along the lines of the above.
This summer, I did have the chance to gift my mother Paragon and Paragon Sleep. And I told her pretty much what I just typed above. I found, however, that she was already very open to it, because we’ve shared health-related resources and practices in the past. Bought them an air purifier, bone broth, etc.
So that’s actually another suggestion I’d give, since it has worked for me. Have a general ongoing conversation with your parents about health and health promotion. It doesn’t all have to be about subliminals. And if you guys connect about other things, it will be easier to introduce something like this as well.