If the Switlik vests are more comfortable and anybody knows how to get one in the UK, please post here.
It's easy to organise a purchase in the USA (using a US based contact) and surface shipping to the UK. Not sure about air freight due to the air bottles, and courier (DHL etc) is a waste of money for anything over say 10kg. If there was enough interest I would be happy to do a bulk purchase via my distributor in NY. Bypassing UK sole agents is always fun
However, I would first make sure that we can get them serviced here, e.g. by SEMS in Basildon.
IMHO that, unless you are extremely lucky, you should plan on being in the water for at least an hour and probably two.
I think, looking at where you will be coming from, at least that long. That's why a raft is so essential.