The offshore operators on the UKCS have to set performance standards for recovering people to a place of safety.
Using a Jigsaw type concept 'creates' something of an issue in that it means that the rescue facility (be it aircraft or vessel) is likely to arrive some time after the incident (indeed quite some time and I'd be interested in just how long it took the ARRC to arrive).
If the rescue resource arrives some time after the incident then there si much less time to recover the people before the magic 2 hour period has elapsed. If they are int he sea they will have drifted apart and they were rumours that the initial Jigsaw trials required quite an effort to reach the point where 21 people could be winch recovered.
Hence the provision of the wrist PLB to allow the aircrafft or vessel to track people.
So if the wrist PLB has 'issues' how does the industry prove it can recover people within 2 hours if they are dispersed in the water - proper PLBs?