I have narrowed down to the Micro-Tron IV and the Source Audio Spectrum. On the plus side for the Spectrum is versatility. The user is able to adjust numerous parameters using the Neuro app, then save as a preset. The octave function is appealing. One of the demo videos features a guitarist playing Shakedown Street, which sounds good to me.
I am sure the Micro-Tron does an excellent job, given the same guy designed it and the original Mu-Tron. I intend to decide and order this weekend.
I appreciate the feedback and comments!