I received my metal bumper case and am giving an update as promised. Understandably there have been many skeptics but, for those of you who haven't been following, I have theorized that the issues with TouchID are related to static electricity (and the evolution of fingerprint scan data) - installing the metal bumper case is an attempt to address this.
With the new case, the first thing I have done is, of course, remove the leather Apple case I had on my phone. In addition, I have gone ahead and removed my screen protector... As electrically insulated materials, I believe that these devices have contributed to static issues that may have effected TID on my phone.
With the new case put on my phone, I have washed my hands, cleaned my screen (and home button), and followed Apple's normal enrollment process for four fingers... Although I believe careful scanning is important, I decided not to do that because I want to get an idea of what effect the metal bumper case has on my TID experience.
So, what have I found? Well, I haven't had the new case on for long enough to draw any conclusions (it's been three hours) but I have made some interesting observations. First of all, after setting up TID, my unlock rate was only about 50% but it seems to have improved greatly over the last few hours as I have played with it. Secondly, unlocking seems to work best when I have part of my finger resting on the case and the tip of my finger touching the steel ring of TID. Thirdly, the case effects the way my finger contacts the sensor because, instead of laying my finger flat on the sensor and pressing down, the case pushes the tip of my finger forward for better contact with the sensor. Lastly, after playing with things for awhile, I noticed that I could get TID to work reliably for up to 20 attempts in a row and then I would have multiple fails in a row... Doing the "Control Panel Calculator hack" would usually resolve this.
What does this all mean? For now, I need to use this setup more to know for sure but TID does seem to be working quite well. There are a few holes in my experiment (such as adding a new case and taking off my screen protector at the same time) but I do have a life and am trying to balance fun with my responbilities. My experiment also raises some other questions: What effect does the pressure with which you are pushing down have on the reliability of TID? What effect does angle have? Could background processes really be having that much of an effect on reliability?
In the end, my answers to these questions will sound subjective but you guys can figure out whether or not any of this works for you. Ultimately that is all that matters because theories are just theories and most of us just want to be able to use our phones reliably. Further experiments are to come though.