There's a difference between passive blocking and surveillance. The former is a safety measure that's perfectly sufficient to keep bad stuff away. The latter is an invasion of privacy that has no benefit, and many unsavory consequences on a child's sense of trust and autonomy. Blockers are enough.

It is a safe assumption that every human, at the age of puberty, will search for porn or sonething similar. If not, your kid is asexual.

A blocker will prevent that search. You know that search will take place. Heck, you did it and at some point in time got away with it.

What possible purpose would you as a parent have for knowing the details of that search? That is just a gross invasion of a very private phase in development. You might as well add cameras to the bedroom to see if your kid, who is obviously past puberty, is masturbating (of course they are - checking on it is just disgusting and creepy).