Test your site using a 2G or 3G mobile connection.
Test it on Firefox.
Test your site with privacy-protecting extensions, such as uBlock Origin, Ghostery and Privacy Badger. If you can, test it with Pi-Hole.
Test it with the Dark Reader extension, because we don't all enjoy being punched in the eyes.
Test it after deleting all your cookies, because that's the first experience people have, and first impressions last. If it's a confusing mess of popups, sort it out.