I have hundreds of recipes in my file that I've never tried, requiring thousands of conversions. Even if each conversion is only done once it's absolutely worth automating.
whatever floats your boat, but it sounds a bit overkill to me.
As a european, I notice how imperial units are sometimes creeping back in. Even hating the crappy illogical mess, you learn to get some feeling just by exposure. Feet divided by 3 is about a meter, and 4 inch is 10cm. A mile is 1.5km.
For some reason I can remember pounds as 1/2 kg, but can never figure out lb without looking it up and finding it is also pounds.
A while ago, a local computer store mixed up feet and inch, and announced things like 14 feet laptop screens. I was the first to tell them, the mistake had been there for a month. It turns out non-USians know what a screen of size 14 is supposed to look like, and the word 'inch' behind it is treated like meaningless gibberish.
Anything that you use often enough can be memorized. A cup of flour is 120g, for example. But I use something like molasses maybe 5 times a year, so I'm not going to remember how much a cup of molasses weighs.
(I use molasses as an example because, due to how sticky it is, I much prefer to measure it directly into my mixing bowl by weight rather than using a liquid measuring cup).