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Single boiler machine - too much faff to do milk drinks
Get a stand alone coffee milk steamer - too much space waste, another gadget to clutter up the place
Answer - nice shiny dual boiler machine which looks great and gets you extra golf club points and saves you X*Y theoretical £3.90 cups of coffee from theoretical local artisanal coffee shop = big theoretical saving.Does that work?
Your girl maths needs some work.
@Dammit has some of the idea but really need to check his working