I need to know if vwo(visual website optimizer) is known to be a drawback with regard to slowing down website load time in any manner?

Visual website optimizer is a A/B testing tool which can help one site owner to analyze his site with a modified of that. It puts a simple code in your website and make a new version of your web page.Then it show one version of your webpage to 50% of your visitors and another ver to rest of the 50%. This way the owner can analyze which ver of the site is generating more revenue & dump the other one.

So my question is can vwo reduce the site loading time somehow?Or what is the drawbacks of using vwo in a website?