Seriously, who needs to record someone without the knowledge of the person being recorded? That’s a big red flag, a perverted character, there’s no other explanation. Creepy Mark Zuckerberg allowed other creepy characters to share personal moments with him.
A know a few people who use them like a gopro - they record bike rides and stuff like that.
But you have misunderstood them - they have a very obvious recording LED, so they’re not designed to record without people’s knowledge. And they have some detection mechanism to tell (by reflected light) if you put tape over it or (electronically) if you break it, so modifying them to record secretly is not trivial.
If you actually want to record someone secretly, you could buy a button camera that an undercover journalist would use for a fraction of the price and not have to do any modification. It wouldn’t upload everything automatically to Instagram though, which I think for the target audience of the glasses is a big appeal…