Well, I have fixed the issue with the TechTool Pro Protogo USB diagnostic/startup drive. I used TechTool Pro to make a 3-pass zero-out erasure of the USB stick before recreating the drive. There's an edit feature allowing more apps to be added to the ones automatically included in the build, so I used it to add DiskWarrior 5. I mentioned this on the forum & a reply from the devs admitted surprise that I'd been able to do that.
So it's all OK now, but initially it wouldn't boot the Mac. So I used TechTool Pro itself to rebuild & repair the drive's directory. After that it was OK.