Oh, yeah... I forgot about that part.
Yes... I am guilty of owning both wrenches and sockets in mm, mainly because every time I get a new gadget that doesn't say "Made in USA", I find that all of the hardware is metric (even Allen screws, which is maddening to me...)
So … since I prefer not to use a crescent wrench if I don't have to, and would rather not bugger up surfaces and orifices using a tool that is "close", I have those as backup... the 10mm wrench being the most common one, I have found.
They tried to get the metric system going when I was a child in school.
I am quite sure that we only kept our "inches-feet-yards-miles" system because it was too expensive to retrofit all of America.
From an engineering standpoint, metrics simplify things enormously... and that is the main reason science uses it. (Moving a decimal point beats fractions any day...)
From a humanistic standpoint, basing a number system on anything is still pretty arbitrary, though I suspect our mathematics work better set up with 10's.
But those arguments are far above my pay grade...