I agree that you do not need two sensors.

The graph is the important thing here, not the guage. Logging with RPM and then reviewing the graphs is the way to go. Things just happen too fast at the time to decipher. As long as the screen on the phone is big enough for you to see all the details then give it a try. It would seem to me that all that info on a phone screen would be a bit much, but my eyes aren't what they used to be.

Even though I have a guage, I log a few pulls and then download them, spend some time looking at what is going on and then decide what changes to make. I make them and then log some more, download them, and then compare them to the earlier logs. That is the only way I can determine what is going on and what my changes are doing. Before and after comparisons side by side.