After many attempts trying all the suggestions in this entire thread, I was unable to get my 2413U working under High Sierra after upgrading (or any other FTDI devices) on a 2010 Mini.
However, I came across this suggestion, which is a little less cumbersome than Jay's procedure and it worked the first time (scroll down to the post by Garrett Johnson):
https://superuser.com/questions/1135730 ... sx/1136084
Cheers.