Which unit is the fun game that gets played. I've seen way to many products right beside each other that use different measurements.

Most people will have devices that can easily convert measurements to the desired unit.

Oh fun, now I can invest even more time and energy into grocery shopping.

That same device can also calculate the unit price (since you know price & weight), so why even print it?

There is no federal law requiring unit requiring unit pricing, but the the NIST has guidelines that most grocery stores follow voluntarily. 9 states have adopted the guidelines as law.

https://www.nist.gov/system/files/documents/2023/02/09/2023%...

I don't think that's correct. Prices for retail goods aren't usually even attached to the product in interstate commerce, and are shown locally on store shelving.

Any applicable unit pricing requirements would be at the state/local level, not federal, but only a few states have such requirements. See: https://www.nist.gov/pml/owm/national-legal-metrology/us-ret...