This step definitely scared me the most after reading all the comments, but with a helper this proved fairly simply. Using two suction cups I pried the case apart from the corner (not directly above the home button), just enough to barely fit the plastic opening tool into the notch. Unless you have 3 hands. Once in, you can release the tension from the suction cups, and simply pry the case open with the tool, to a satisfying pop.
I used the zip tie trick, which is a clever idea. I don’t think it was necessary, but I would probably use this precaution again.