Probably not an issue with Boot Runner per se, but it would be nice if I could get it to work.
Replaced Fusion drive with an SSD on a 2015ish 27" iMac. Left the small SSD part of the Fusion drive in the machine, Disk 0. Installed High Sierra on the new SSD, Disk 1. BCA is unhappy about this arrangement and refuses to help, so I formatted the small SSD and installed Win 10 manually. All is well, except that Boot Runner displays the Windows drive, lets you select it, tries to restart into it, but fails. Boots back to macOS and lands at Boot Runner screen.
Hoping someone can confirm my suspicion that the drive configuration is not going to work. I can still Option-boot into Win 10 or macOS with no problems, just not with Boot Runner.