So I guess you can visualize "the metre has been officially defined as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second." I can visualize many things, like electrons (or holes if you like) flowing in an electrical circuit, but to visualize how far light travels in 1/299,792,458 of a second is beyond me. Your definitions for an inch can be easily visualized for a rough estimate.
I have no problems with English (Imperial) or American units, nor with SI units. I work in all three. Have taught (for 19 years) engineering/technical folks in both Imperial and SI units for years. Converted many tutorials, lab assignments to SI units as we adopted SI in about 1979. Re-derived formulae using SI units. Have worked in the EPC industry for 20 years using whatever system the client wishes to use. I can flip back and forth at will. You should look at Pipe Tables if you want to see a real mess. No one is ever going to change the dimensions on 2" pipe, nor the threads associated with it. But 2" pipe is called 2" pipe, though I see some people trying to call it 50mm pipe. But that should be 50.8mm pipe! Makes a lot of sense doesn't it! Also pipe thickness is given as Schedule 10, 20, 30, 40, etc. No reference to Imperial or SI. It's just a crazy world.
I still think the best conversion system for those without SI Metric abilities is to use 2 rulers, laid side by side. Gives excellent visualization.
Tom