The appropriately estimated quarterly routine delivery and quick water-check when they deliver, and delivery person's quick report to service tech for repair/part if they find a problem.
In-office staff's ability to understand a question.and troubleshoot by phone even when we talk like this, "You know that thingee that's on the tallest container that goes into the pipe where there's another pipe above it? Oh! And our water heater is by it." This seriously is a BIG deal!!
Quick response any to trouble or simply a question that may arise.
Overall, it's a trouble-free setup due to quick and accurate response to any issue.