I am getting voice training from some graduate students, and last semester they were actually students of Kathy Perez. They had me using the Eva app, and I found it very useful. I don't think it's useful all by itself, but when combined with other training, it's useful. I use the Eva app to calibrate my voice higher, and then I try to speak phrases in that pitch. I find that using the Eva app that way raises my base pitch fairly considerably. It's best to combine that practice with other stuff, like resonance training (trying to move your voice up into your face, instead of your throat).
It's important to note that a major difference between sounding passable and not sounding passable is voice quality. Without quality, a higher pitch just sounds faked. If you watch some videos on resonance, that will probably really help you maintain quality while you use the eva app. If you can raise your pitch with the app while maintaining vocal quality and then do exercises, it should help.
Another important thing is that the Eva app has you practicing pitch at 220Hz. My teachers tell me that it's not realistic of me to think that I will talk at that pitch, but that learning to maintain quality at that pitch will cause me to normalize to a passable - if somewhat low for a woman - pitch. Sounding kind of fake at 220 is fine, because that's just training.
