My ISP's support told me to always use their local copy (https://speed.aussiebroadband.com.au/) as it avoids routing issues downstream but more importantly, it logs the history onto my account for them to view.

The numbers are often higher than what I pay for, but I think they are honest. When I was having connection issues (dialup-tier download speeds, 20 megabit upload) it was reflected accurately. Since I trust them, I like this arrangement. If I didn't then I wouldn't.