"Yes that makes a very nice (a little expensive)installation, but you'd better put a switch in that W/P Extension Adapter"
In a public place, ( such as this looks like)...I don't see any other way to install this. I'd wire this just like it was a "insta-hot" unit, which are almost always located directly under the sinks.
GFI or no GFI...I would never cord and plug this installation. How do you tamper proof a corded unit?
In regards to the "switch"....I've always treated these types of units similar to restroom hand dryers. If you have to service those, you'd be tagging them out at the panel. ( since you can not install a switch)
But as usual, I could be wrong regarding all of this...
Regards
HP