A large site that I worked on found a huge SEO difference between products with lots of long reviews and products with no reviews. There were some products that we couldn't seem to rank for no matter how many times we linked to them internally. It seemed to us to come down to user experience. When we didn't have reviews, users would often bounce. When we had lots of product info including dozens of good reviews, the bounce rate could be as low as 10%. On the other end of the spectrum, the bounce rate could be as high as 70%.
We had the text of the user reviews directly in the page. It often helped talk about the product in a natural way and introduce keywords that the manufacturer didn't think of.
I'd recommend user reviews in the page. Users can find them more easily there. Unless they are duplicate content (taken from other sites), or unless they are too low quality for users to find useful.