> using em dashes despite space-separated en dashes being more popular is another (though that one varies by locale)

Okay so I was told in my English writing class that in US English one uses the longer em dashes without spaces. But I just can't get over how they look, and in German we use en dashes with spaces (AFAIK), so I usually do that when writing English except if it is a paper where my advisor will complain if I do. ;)