There was no real goal beyond the experience of building the thing and making it work. I use them to monitor stuff like fridge/freezer and HVAC intake/output, and as leak detectors in my crawlspace.

As you'd probably guess, the fixed cost of the manufacturing was extremely high. Unfortunately I didn't write the numbers down... but going from memory, ordering 5 instead of 30 would have only reduced the total cost by ~20%. I remember a weird valley in cost-per-unit at a quantity of 30: my understanding is that JLC combines small orders, so my guess is that 30 of that board was the largest order they were willing to squeeze onto the same panel as another one.