Real User Monitoring gives insight into performance for actual users visiting the website.
https://www.pingdom.com/rum/
Analytics and Tracking · Application Performance
Get access to data on 613,807 websites that are Pingdom RUM Customers. We know of 264,650 live websites using Pingdom RUM and an additional 349,157 sites that used Pingdom RUM historically and 250,151 websites in the United States.
Get a list of 613,807 websites using Pingdom RUM which includes location information, hosting data, contact details, 352,821 currently live websites which includes 88,171 domains that redirect to sites in the list. 349,157 sites that used this technology previously and 250,151 websites in the United States currently using Pingdom RUM.