It's worth noting that this technique only works if the target user is using a mobile app (not web) that's been granted persistent location sharing permissions. The app also has to support one of the ad networks allowing the targeting they used in the paper. They tested this with the Talkaphone app, which requires (not requests) persistent location sharing.

I'm not sure, but iOS's anti-ad tracking function(s) may have an effect as well (https://support.apple.com/en-us/HT202074)