How noisy is it? I heard of people installing them, and getting complaints from the neighbors.
The exterior unit is basically silent even when there was a cold snap (below freezing but not northern alaska cold).
I suspect an interior air source heat pump hot water heater, being smaller, will be noisier, and likely less efficient.
I'd love to switch my 240v/30a water heater to use a 120v/20a service, but will wait a bit longer for the technology to mature. Ideally it'd have the heat collection part outside.
Outdoor noise is less of an issue in the winter in big cities because windows are closed.