Okay, personally I think its pretty ridiculous how many people complain about this app/website. They're very straight forward. Their ultimate goal is to exchange products in return for your honest opinion.
HOWEVER there is no guarantee you will get anything. Here's the thing, if they send out a product in exchange for a review. They want that review to actually be seen/heard to advertise the product. So a big factor of you receiving a voxbox is based on your impact. And they also want quality reviews. If you're posting short vague reviews it's likely that you won't get picked often.
If you put in the time and effort to build up your impact score and write quality reviews, the odds of you receiving a voxbox will increase! It may take a while but you are getting it 100% free.
I personally have earned some sweet products, that I love!
If you're willing to actually work at it, then it's worth it!