The total numbers haven't been posted as the USN posts have still to be confirmed. Off the top of my head there were 6 aircrew went to Canada on loan (retrospectively annotated as Seedcorn), 7 to New Zealand, and 2 to Australia as acoustic liaison officers.
The Aussie seedcorn aircrew are not in a flying role. All selected personnel were required to sign a return of service of their overseas tour plus 2 years on return to the UK.
The USN seedcorn selection is still a work in progress.
Although the Seedcorn initiative may be merely a token gesture, the experience would definitely required should the UK procure a MPA in the next five year or so.