Did this one last year. Nice bit of current at the start. & a great strating system , All on the quayside in your wave (4 waves ranked on speed, slowest first) gun goes & you all file over the timing mat down some steps & away, very civilised. No mass brawl or biff like at a tri start.
Found navigation difficult last year, all over the river, crashed into rocks twice, tried to swim up a tributory, almost missed the 2nd feed station. & when we hit the tidal bit it was really choppy with a head wind. Its a nice event but I'll only do it again if I thought I'd survive without the rubber. Last year it was about 12 degrees at the start, so too cold for me without insulation, but quite a few go 'naked'. Just about full by now though I think!