The mica line doesn't get carried along with the swirl- you'll get a broken mica line and tiny bits of color strewn around the soap. Most of the mica gets lost.
I had good luck with a pencil line in a very simple swirl. The pencil line was with Activated Charcoal and not mica, so I can't say for sure mica would work as well, but if you want to give it a try, this is what it looked like right after the cut. (The ones on the right.) I was pretty happy with it. Sorry, no photos of the finished soap.