Thanks. I can see a company like Open Tracking hire out event trackers at something like £5 + VAT/runner, slightly more for premium, and some individuals hire them for challenges as well.

Tracking down at this level wasn't even an option until recent times but I can see how useful it could be for the long distance fell races like Ennerdale or Wasdale if somebody goes seriously wrong or has an accident. The race organisation would then have a smaller area to cover if they needed to initiate a rescue search. That's when it would be most beneficial. Maybe it will be used more in future years as the sport evolves ...?