It's a very interesting design.
Here's a cost comparison video.
$1500 Heat Pump Water Heater - Worth it? - YouTube
And an "Ask this Old House" video on a Florida installation.
How to Install an Electric Heat Pump Water Heater | Ask This Old House - YouTube
A drawback it seems would be in houses that have the existing water heater in the conditioned airspace along with the HVAC air handler you would, I imagine, have to move it out into the garage itself. And I'm not so sure in reality how much garage cooling it would actually do for those interested in that aspect.