So I went to the Boat Show and bought a RescueMe EDF1 LED flare. I had intended to buy an Odeo Mk3 as recommended by PBO because it is simpler to use - just twist the base to turn on. However if you twist the base the other way it would appear that the batteries fall out! I'm sure everyone else would twist the base in the correct direction; however for me, in an emergency, Sod's law would apply.
Compared to the Odeo, the RescueMe is cheaper (good), smaller (good), slightly brighter (ref. PBO, good) does not take standard batteries (bad), the supplied batteries have a 10 year shelf life (good; may well see me out). The cheapest price I found was from Cactus but check they do give you their Boat Show discount price - there was some confusion as to what I was charged. I still also intend to buy a personal flare pack (which were not available at the show).
Colin - I always do carry the PLB as a "long range" distress device... my references to mobile phone, VHF, and indeed, flares (LED or otherwise) is for guiding the approaching rescuer towards me (and in the Solent that means finding me amongst all the other yachts!). I did ask various sales-people at the boat show about the effectiveness of a PLB operated from in the water and they all said it would work perfectly well - but "they would say that wouldn't they"!
And of course, my hope is that buying the RescueMe Flare was a total waste of money!
Peter