Invigorated by a gratifying Melbourne Cup day & Bribie's post I will give my 2-cents.
Over many years I've done, in the following order, chilling with ice, copper immersion chilling, 30-plate chilling & am now back to immersion chilling again but using a ss immersion chiller for the following reasons:-
Ice chilling is obvious (in the bath, whatever), copper chiller worked well with my young (ATT) HERMS but was a ******* to keep clean externally & so progressed to a 30-plate ss chiller which worked magnificently until the day that I realised, being so close to the beach, my bore water was slowly but surely corroding the copper welding in the ss plate chiller with the unenviable results & so progressed to the final solution of the ss immersion chiller .
Cut a long story short, I run the salty bore water through the ss immersion chiller. Stop/progress according to my '0' chill additions then chill down as far as the bore water will take me (around 29/30 deg c in summer) then switch to a 1 x 2-litre ice cream container of frozen water sitting in just enough water to submerge the pond pump in a
tilted esky until I reach equilibrium (usually around 19 deg c +/-).
This is fine for Ales. Lagers usually take another 2-litre frozen water addition if I want to bring the temp down lower.
Please note that
tilted is good as you are barely covering the pond pump intake & thus need minimal water volume to keep the ice icing on as it were.
My 2-cents.
PS --- Please take it as read that ss immersion chillers work excellently in normal circumstances away from a salty environment.