Nice tool! When I run it I get solid red blips at the 2000 ms level after just a couple of seconds. Here's what it looks like: https://imgur.com/a/bTA86qz Is there something strange going on with my network or ISP? fwiw, I'm running Brave on a Win10 laptop.
It doesn't work with HTTPS because the pings are done with HTTP requests. You have to disable HTTPS-only mode and load it over plain HTTP: http://gfblip.appspot.com/
Requests get blocked for mixed content after a few seconds if the site is loaded with HTTPS.