It is one of those crazes these days, to offer reviews of other sites.
While it can help you make added money, it is also a lot of work to visit, review what is there, then to put into easy to understand words.
Add credability to your reviews.
Actually be different than most out there, give your members honest no holds barred reviews.
It can only help the trust factor, which translates to income for you.

It is about Trust.
While everyone wants to make a sale, at what cost?
The more honest, more real your reviews are, the more trust you build up with your customer.
That keeps them members.