It's not about signature participants using the product, it's more about bringing people through signature participants that may use your product. In advertising industry, we see popular people advertising the products, they don't use the products they promote but through them product gets known to the masses.
I agree with the point that @Royse777 made, if you ask someone who visits this forum give me some examples of crypto based gambling sites and the first thing they are going to blurt out are Stake, Roobet, Duelbits and so on. They are not going to say BetMoose which is a Canadian mutual betting platform that I know about but very few people here might. Then there is idea of constant bombardment with the banners so to keep the same thing in the users memory even if they dont use it at all.
Review campaigns serve a different purpose, I would like to add to my previous comment that after reading some comments in this thread I have felt that reviews are paid here and hence they are going to unorganic and having a biased opinion. That does not mean they dont help the project, but should be taken with a bit of salt for a consumer.