"I'm looking for some information and informed experience on helicopter ice detection systems...
such as which ones are reliable, which ones aren't worth jack, how much warning they give you before the aerodynamic affects are noticeable.
Any info much appreciated."
I'm flying Super Pumas certified for flight in known icing on Canada's East coast, but flight in severe icing is prohibited, which we consider any freezing precip.
As far as detectors I've flown with many of them and none seem to work, giving warnings in clear blue sky and no warnings when we have inches of the stuff on us. The best indicators are the mirrors and wipers, and of course the torque, which will initially climb about 3 to 4 percent if you neglected to put the kit on for any reason. Having flown S61's out here at night for years watching for that torque rise (we would not go out in known icing of course, but forecasting being what it is, you sometimes encountered cloud below zero you couldn't see at night) I must say a certified for flight in icing aircraft reduces my daily stress considerably.