If you are reviewing a piece of hardware such as a motherboard that has some major defects it is good to let people know about them before investing the money in this motherboard. I would write up my reviews and your finding very carefully to not accuse the company of selling defective items that they are not willing to guarantee.
This holds true for any type of a review site. People have strong opinions about certain things they buy and also high expectations about how it should work. If it doesn't work like they think it should they will tell the world about this. A company can't sue this person for their personal opinion, all they can try to do is work with them to correct these problems to try and make the person happy again and hopefully change their review.
There are a few review sites that have reviewed money making sites online and called these people rip-offs and scammers. They had many issues with the lawyers from these companies because of how they wrote their reviews and what they said about the companies. I read a few people who had lawsuits presented to them and lawyers asking for thousands of dollars in damages. Other people wrote a review about the same site, but they chose their words carefully and didn't have any problems with the owners of the site.
This will basically depend on how you write up your reviews and how you report your finding. Just chose your words carefully and don't call this company a rip-off. Just make sure that people understand that this is a defect and the company didn't realize this when they put this on the market. It basically boils down to how you present your review and how you chose your words.