I guess you just had to give your opinion about their project and he mostly want to keep the project stay anonymous for not giving enough information and that's why he wants you to submit the review through PM but it's better to be sure of what he's offering. But in what I can see it's sort of bumping an ANN thread I guess and if my instinct is right, better not take this.
Bump topics are not needed - just one review from one person about project in ANN thread.
We might get tagged if we advertised a scam project so disclosed the name of it.
We pay for the review, not the opinion.
The list of arguments that say that the project is a scam is also a review and we pay for it.