When I was working in Virginia, some counties required that civil engineering drawings be submitted in metric units. Within a year, those counties converted back to English measurements. They found that the metric measurements could never be "pure," because all of the previously designed and built stuff was in English units - the nominal inside diameter of a 24-inch RCP drain pipe, for example - and no manufacturers were making metric materials that matched the English sizes. A metric-sized pipe might be manufactured as a 500-mm nominal inside diameter. What we needed to tie real proposed drains into real existing drains was a 457-mm diameter pipe. Who's making that?
In the meantime, the requirements became a drafting hell, since we ended up having to put text and labelling for both systems onto the plans. Talk about clutter! And who really wants to deal with a proposed utility easement across a piece of property that is 7.33 meters? It was a paltry effort to keep close to the English equivalent requirements. It failed for practical reasons, and these counties soon changed their requirements back to English.
Personally, I only prefer the English measurements because that's what I've worked with most. But when I have had to do metric, I'm fine once I get into it. Mixing the two in a project is an abomination.