The site, like many out there for businesses, is legal. However, you may want to monitor the posts for anything that could be seen as defamation or as posing a danger, meaning anything that uses profanity, makes threats, etc. Defamation involves a false fact being told (not an opinion) to others with the intention to harm.
In your case, this should not be an issue as these will all be opinions (however, if someone posts that so and so has some disease, etc., you would be smart to remove it as it is not something that they can probably prove and it doesn't go to the reason you have the web site).
I would also put up a disclaimer on there that the posts are only opinions of the individuals posting and not the opinion of the site (meaning you). Also, I would make sure there is a disclaimer for people who are posting that they have the liability of anything posted and not the Web site.
Please press Accept if this has helped.