Many very powerful and desperate people really don’t care how protected the witness is. Their future depends on the witness not testifying about what they know. Of course, there are many ways to persuade someone to not testifying or to lie.
I have no idea how effective it was for the campaign. It must be hard to measure the effectiveness. My wife uses it with her business, and I was rather surprised how much FB knows about users and how narrowly they can target ads.