When you say myriad you don't need to say "of".I'm 53 and I use a mash of metric and imperial. A different mash to you. I measure people's weight in metric but their height in imperial, for example. I can convert between metric and imperial for casual use. Anyone who can use the hilariously over-complicated imperial system with its myriad of conversion factors and numerous different names for different units of the same type (e.g. off the top of my head I can name a dozen different imperial units for length) could convert between metric and imperial for casual use. It's just another couple of conversion factors to remember.
But for anything serious I'd use metric. It's a simpler system with less scope for errors. Also, it's standardised globally. Older systems of units weren't. An inch in one place would be different to an inch in another place, for example. That's why Napoleon is famous for being so short. He wasn't. His height was given in French feet and inches, which were longer than English feet and inches.
Hmm...could I name a dozen off the top of my head? Barleycorn, inch, foot, cubit, rod, ell, yard, furlong, fathom, mile, nautical mile, league. Yep, there's a dozen.
Old systems of units made sense in the past. They were locally standardised because the power to decree standards was local. They were based on things people could check easily, which is why the British imperial units of length are based on grains of barley. But that was the past. Metric is simpler, globally standardised and easier to work with.
P.S that was a well meaning message, not being a troll