The difference between targeted ads and untargeted is like the difference between alpha and beta, or index funds and hedge funds. It’s not that a hedge fund doesn’t have better risk adjusted returns than an index (they usually do), it’s that the fees are so high it’s usually worse net of fees.

There was a study posted on hacker news that targeted ads have something like a 5% higher conversion rate than untargeted ones. The problem is that you end up paying 30% more compared to the commodity service. So unless the fees go down or the efficacy goes up, it’s not worth it.