I want to add a section to my news magazine website. So far I only display news. But I believe adding product reviews will enhance my site. My site is in wordpress.

Question is, should I make this product review section under a separate domain name and just give link from my site? Or, should I keep it under the same domain name of my site and make it as another category?

Note: I have a very good spare domain name which has the word "review" and the relevant product in it, if I want to use a spare domain name.

I am asking in terms of SEO and also attracting visitors regardless of SEO, is it better to have everythign under one site?