why hold it overhead? I've never had to do that
Not always "overhead" but definitely held out there with extension and definitely at or above chest level. It's because if the RO can't keep up with the shooter because of an unexpected fast movement, the following shots are more likely to be registered than if the RO was carrying the shot timer on his belt. We learn this in our IPSC RO course. Watch the following video of the various ROs following Eric Grauffel in Greece at the last world shoot:
This RO technique would probably be even more important for .22 AR conversions, unless of course your shot timer is set for airsoft sensitivity. But then you better pray that the shooter in the next bay is shooting airsoft too
It's just not realistic to think that a shot timer will face the same level of "non-abuse" as an iPod or Laptop or LCD TV. Therefor it must be made to a higher standard of durability than consumer electronics meant for less demanding environments and applications.
Aside from that, I just noticed which timer was being used in the Eric World Shoot video