Google loves personal content
Besides, search engines really value reviews, both in quantity and quality. They tell Google and its users that people are interacting with your brand, it makes the social relevance of your products and services reliable. Eventually it will help you rise in search rankings. Someone leaving a review will be evaluated as unique content. The more reviews are written, the more content Google collects, the better your brand will be assessed. In the end, it's better to have a lot of honest reviews with some criticism - nobody, and no product is perfect - than a just a couple of 5-star reviews. Having only a few top reviews will look unreliable as well.