QOUTE: "supply on demand system"

That could mean two different systems. 1- hot water stored in a tank
and ready to be used. 2- hot water made at the point of useage.

Both systems are available, but the storage system is more costly to
have hot water and the water in the whole house piping will cool
meaning, more wasted water to get too the hot water and the system
is a lot more costly to install. The storage system type cost to
maintain the temp. you set in the tank also.

Having units where hot water at point of use means less wasted water
and only cost when the water is turned on and you still control the
heat, from cold though the warms to very hot. Plus only one water
pipe is needed and you have the choice of turning the unit on or not.

The whole house system if it went down, there’s no hot water
anywhere in the house until it’s fixed. That system is used in the
USA also.

The point of useage systems, (hot water on demand), have been used
in the EU for many decades. The 1st unit I install in a Peru jungle
camp back in the 80’s, (shipped in), was a shower head you wired in
and the temp. contol was the water flow. Now, you can control the
heater in the unit plus water flow.
B-Ray