True "open source firmware" where you can inspect and modify everything on a network card is going to be rare if they exist. However, Linux has mature open source drivers that interface with the hardware for consideration and the output can be monitored at a gateway/router.

These strawman arguements aside, I think the author's point is that the purpose of this tool is for privacy of network connections and as such deserves scrutiny.

To your point, open source does not equal secure. We still have to trust that someone more familiar and with interest has reviewed the code and humans can still err.

The author provides links to an open solution that has already existed (albeit not as polished) and explains his other solution blocking at a DNS level.

The problem with a black box network monitoring and blocking solution is we have no clue if there are rules we are unaware of or if all information is being provided in earnest. Ultimately this tool is hosted by a business selling other privacy conscious applications. I know If you're good at what you do, don't give it away for free.

Ultimately, everyone is free to choose their own solution but the article cautions of the hype that's emerging around this tool when other solutions have existed that are more transparent.