Are you concerned about latency of vendors on your page? I would highly recommend trying this free tool @ Webpagetest.org. It offers a free service to check performance on your site. Webpagetest.org can be very helpful as a basic tool in identifying issues in the website configuration and for monitoring performance of specific vendors that are active on your site. Before signing up for a paid monitoring service I would recommend trying this tool and understanding what your performance measurement needs are.