Besides, this call happens only once for each visitor. After the first visit, the script is cached and will not be download again for next visits.
Also, we noted a very weak CPU loading for visitors subjects to an A/B test. To guarantee this aspect, some old versions (especially Internet Explorer 7 and before) are eliminated from the tested traffic. It does not impact the usual navigation on your website, visitors using those versions are simply not included in your A/B test.