I have basically both sets of tools. and "Yes" it's still a 3/8" drive and 1/2" drive ratchet!
I guess I'm too old to put the metric system in my brain's visual understanding of things. My only quick reference is 19mm or 3/4s of an inch. I can usually identify an SAE fastener my looking at it and 80% of the time grab the correct wrench. That's what I'm talking about.
I can see a yard in my mind but ask me to frame that into a meter and I loose a little in the translation. KM and Mi and even more challenging due to the visualization I have in my mind. I know a Km is shorter buy I just can't feel it.
Working with metric sizes is almost like a computer working with binary. For most of the world's population metric system is great however just make mine 33/64th and I'm good with that!