[CarlG]

Voice of experience here:
On a tour a couple years ago, one of our members had a failure with his dizzy. Not sure what the problem was, but he wound up just replacing the dizzy with a spare he had along. Then spent the next 30-45 minutes trying to time it correctly. Finally, I asked if anyone had one of the Nu-Rex tools. One magically appeared from the depths of stuff the several guys standing around had. Using the Nu-Rex tool, I was able to time his dizzy and get everyone back on the road in 5 minutes.

I now carry one in my tool bag all the time.