I am only able to provide support for the Site Reviews plugin here. For assistance with the Review Themes addon, please use the support form on your Nifty Plugins account.
Random reviews are great in theory, but since PHP is a server-side language (not client-side like javascript) any caching you do on your website to speed it up will make the randomness no longer work.
You can use this code snippet to add a new [site_reviews_random] shortcode to your website. This shortcode will display a random review. All of the [site_reviews] shortcodes options should work in this shortcode except for pagination which is disabled.
Be aware that if you are caching your pages or using any kind of optimization/caching plugin to improve the speed of your website, then there is no point in using this shortcode since the random reviews will be cached to the page.
