I don't have a switch, it is clearly temperature-controlled.
As I said it works in that it shuts the PC up when idle but there is no silencing at all when things get in motion. Keep in mind my environment is very quiet otherwise, other people would rate the full-rpm noise as nothing special. But I do.
I think the main advantage here is that the NV silencer gets the air from the GPU, including the GPU's RAM, directly out of the case. That is a huge advantage for the rest of the system.
I don't have any reliability problems, but this product is not for me. It is a power thing, not a silencing thing.