Well in the short time since my previous post I found the following on the Aireon website:
Position Updates
Unlike traditional en-route radars, which rotate once every 12 seconds, Aireon’s space-based satellites can provide position updates up to twice per second, with an expected Update Interval (UI) performance of eight seconds, which would meet the five nautical mile (5 NM) application needs of en-route separation services, according to EUROCAE ED-129B and Eurocontrol GEN SUR specifications.
https://aireon.com/resources/technical-overview/
I apologise for the bum steer in the debate between the two systems.