Personally, I feel that review campaign brings more results to the project owners because the participants of the review campaign will surely use the project and there is the possibility than more than 30% of the campaign participants will continue to use the project if it is a good project.
Whereas, we can say that upto 5% of signature campaign participants doesn't use the project they promote.
1) campaign manager's perspective, managing the reviews campaign will be easier, and the number of posts he will read will be fewer.
2) Users: it is less valuable as you can get $50 from the reviews campaign, but signatures campaigns pay more. as a user, if the choice is between a reviews campaign and a signatures campaign, you will choose the signatures campaign because it means more payments to you.
3) project owner, the number of people who visit the forum without logging in is large, and in the reviews campaign you lose all these potential users, which is possible in the signature campaign.
The campaign manager does less work on review campaigns, users get paid less and the project gets fewer views and therefore fewer clicks.