[narcout]

Could internal (therefore not easily detectable) verdigris be a concern?

Doesn't the beer stay on the exterior of the coil? Unless you are returning the coolant to something you are consuming I wouldn't see this as a problem.

Yeah, that's the case when using an immersion chiller, but I was referring to the statements above about HERMS coils.

[beerocd]

It doesn't matter at our level, they both do well. I have one of each, the biggest difference is the rate of the water flowing through it. I used to recirc with a pump - then I brewed outside last session with a garden hose connected.  Wow was that fast!