This is as accurate as my genuine Peterson VS-II tuner. I think the display on the iPhone is better, because it is clearer and brighter than the one in the VS-II. The display is somewhat jumpy, even for somebody who is used to a "real" Peterson tuner. The noise filter is pretty good, and the input gain control is nice to have. I have used the Peterson 1/4" adaptor with an electric guitar, and it works fine, as well.
If Peterson will be doing updates on this, I would like to suggest that they put their "sweetened" tunings in, along with the Buzz Feiten tuning offsets. They may want to look at some sort of software dampening, switchable if possible, to keep the display a little more stable. I dont know if putting in the various temperaments would be possible, but they may want to consider the temperaments as add-ons at extra charge. That way , the base software package can stay cheap, and people who actually want the added temperaments need pay for them.
Kostas