The inexpensive ways to measure hardness are colorimetric: you add some reagents to the water and look at the color. Electronic colorimeters exist but are not particularly cheap. Electronic colorimeters with automatic reagent dispensing also exist and are quite expensive. And you need reagents.

I’d rather save $500 or more on my dishwasher and type in the hardness. Even without my utility report, hardness tests are cheap if a human operates them.

The main annoyance is the fact that there are a couple different units for hardness.