For your specific scenario, there are many benefits and really can't see why NOT to use them. Basically, you want to have user's reviews, so while users are not the focal point, they're an important aspect of your site, if not THE MOST IMPORTANT. and this is NOT an exageration.
I assume your app is oriented to sell. Now, with apps like yours, I can find 100 places that sell pizza. As an user, I'll start to search for proximity, price, flavors and such. Then I may get (say) 10 places that fit into the criteria. As an user, what will decide my purchase action? REVIEWS! See how important this is?
Another example: informercials. They all have reviews and users swearing for their benefits. In an objective way, we all know infomercial products are usually low quality, cheap and a waste of money.... Yet all those people can't be wrong, they are so happy with the product I want to buy it too!
In short: pay special attention to this part, and YES, avatars are a fundamental part, because it provides a sense or a real person sharing his/her experience, and users can see it at first glimpse.
I won't extend more, since I could be explaining benefits of this approach for hours, just take a look to this page for more info on the subject