It’s really easy to learn the size of your body. My span is around than 20 cm. 5 of them is 1 meter. the width of my pinky is 1 cm. You can learn how to step 1m distance, for me it’s a bit longer than a normal step. I can measure with my body between 1cm and several meters. So it’s really easy to overcome this small limitation of the metric system.
It’s as easy as getting comfortable with the usual measures of your body. I also know how much is a kilogram because I can lift a big water bottle which also is a liter. Really, the way all of the units are built more or less around water can give you a pretty accurate instinct.
My feet are certainly not a feet long. More like 25 cm or so. But as another commenter already said, I can measure ~175 cm using my arm's reach easily, matchboxes are standardised as 5 cm long, the width of my palm is about 8 cm, distance from my fingertips to my elbow is around 50 cm and the distance from ground to approx. my navel is 1 meter.
Plenty of ways to get an approximate metric measurements without a ruler or measuring tape.
And it's much easier to convert from cm or mm to m (or vice versa) than to convert between ft and inch or ft and 1/8 of an inch or whatever weird measuring standards the US-ians use.
In most cases, the American spelling of English words compared to the rest-of-the-world spelling is pretty much a wash. A matter of personal preference.
But “metre” is a hill I will die on. “Metre” and “meter” mean different things, and by spelling them both “meter”, as the Americans do, you’re just making communication worse.