The thing is: It
isn't really based on human dimensions. Some people's feet are about a foot long - but most people's aren't. The chain? Yes, very intuitive - although I prefer the standard "piece of string". The furlong? errrm a long furry thing?
No, I disagree. The old measurements were based on human dimensions, but in the vast majority of cases there was no need to be absolutely precise. A foot is about the length of an average adult foot, for example. A mile was a thousand steps (the Roman
mille passus), again variable with stride length, but a useful concept. There were plenty of more precise measurements (troy and avoirdupois ounces, drams and the like for commercial purposes, for example) for when accuracy was needed. But for day-to-day transactions, 'about a foot', 'about an inch' and 'about a mile' were adequate. A furlong was originally a 'furrow-long' - the length of an average furrow in a field. In a society where the majority of people worked on the land, that would have been a useful mental image to describe a distance. Again, originally it would have been an approximate distance, and only became defined as 1/8 mile or 220 yards much later. Agreed, the more people needed to calculate rather than estimate, the clumsier and more frustrating the old system became. But its basis in human factors is why I think people feel comfortable with it.
But like you, and I'm sure many people, I'm entirely happy with either because I've dealt with both a lot. With some exceptions: My bathroom scales are marked out in kilos and stone, so both make sense to me. But any weight (of people or things or stuff) expressed American style in pounds makes no sense to me at all.
I'm with you here. I think of my weight as 'something stone something' and always have. If I'm watching it go up or down, I tend to measure in kilos for all the obvious reasons. But a 200lb person - are they ridiculously skinny or a lump of lard? I'd have to divide by 14 to have a clue to the answer. 2lb of flour, no problem. 200lb of adult - reach for the calculator.