That's a good point. I've already seen at least one other person on this post comment to a Github repo that blurs faces. It might be secure, it might not be. I wouldn't trust it by default.

With a static overlay, the method is simple enough that I can evaluate the security. With a blur, I don't know the difference between a good one and a bad one, so I can only trust the reputation of the author.

I like to be able to look at the output of an anonymizer and to be able to tell myself at a glance whether it worked.