Does anyone have experience with Visual Website Optimizer and its influence on loading time and user experience? With all these Javascript A/B testing services,

Does anyone have experience with Visual Website Optimizer and its influence on loading time and user experience? With all these Javascript A/B testing services, I'm worried about content flashes and long loading times. E.g. for the JS redirect, the browser would first load the page, THEN execute a redirect, then load another full page. Or the content might change after DOM completion, delaying rendering, or after rendering, causing flashes.