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.
I'm not sure where you get these numbers from. Is there any questionnaire or research that talks about this? From my experience, I tend to use the service I advertise on my signature occasionally to make sure it still works properly while I tend to forget a project that I reviewed unless I really need their service. If your number is legit, wouldn't you say that the signature campaign is better at customer acquisition then? 5% of participants don't use the project means 95% continue to use them, no (assuming the participant number is the same)?