I personally prefer to do it that way--you can create a more convincing review that's more likely to make sales. It's not always possible or practical, though; for example, would you break up with your significant other just to test a product for getting your ex back? ;-) In cases like that, or if the product is expensive, it's usually best just to use the vendor's affiliate resources instead.
Its amazing of the many affiliate programs that are out there where people are making a good living from them. For example the few that you mention that has such a great training model, wealthy affiliate tops them all because of the way this business is structure and I believe that wealthy affiliate has the best training program in the world when it comes to affiliate marketing. Thanks for sharing.
If the answer to each of these questions is a resounding yes, rather than jumping to conclusions immediately, take time to research whether or not others are out there making a sustainable affiliate income from products and content in this niche. In a sense, competition is a good thing here—it'll help you validate your idea and prove that it's worth of building a business around.