I just wanted to add to the existing commentary regarding the FTDI Driver issue.
I upgraded and this was my experience
Mac Mini 2012
New SSD [blank]
Install Mojave
Install Indigo
Plugged in RFX and 2413u into the same USB ports that they previously occupied
Re-Booted Mac
No issues at all. I didn’t even have to re-select the ports from within Indigo!
If you own a 2012 Mac mini, please read this warning post:
viewtopic.php?f=133&t=22047