You know, I was at the Sun 'n Fun airshow at the end of March (I was helping man the GlobalNavSource booth). Those other apps were also in attendance, and I answered that question a lot :)
WingX and FF are both great apps, but one main thing is we really tried to tailor the app to in-flight use, as opposed to preflight planning. You can see this in how we did the UI to give the pilot fast access to the plates (swiping and sets of favorites), and also in how we do the search features (autocompleting searches, nearby and recent airports).
We also have really great maps, and part of this is a legacy from approaching the same problems in both the marine and hiking apps we have worked on. For example, we can compose any base map with any overlay in our app (i.e. VFRs + METAR data, and in the next version of the app, VFRs + METAR + radar). EFB also nicely does a course-up view of the map, which lots of people at the airshow appreciated.
Ah, aren't you the guy who admitted to the ForeFlight founder at the show that you copied their app? I hear you're in for some courtroom time . Why don't you post some screenshots of your airport page and their airport page side by side so everyone here can see your "original" work.
Private pilot here(I don't fly jets but I've have been trained in instrument flight rules so I can talk about the chart). It simply depends on how well the various approach plates(i.e. the diagram shown) or other things are shown on the map, and if multi-touch zoom is supported.
If they are, then this would be awesome. It would beat the crap out of having to flip through a book to try to find that one specific approach plate. Typing a few alphanumerics and having all the frequencies show up is so much nicer than flipping through Airport Facility/Directories.
In addition, you can look at plates or airplane sectionals and see that there are a number of items printed in small type and multiple colors that pilots have to contend with. If you want an example, try http://skyvector.com . Someone with flight knowledge can tell you what each of the symbols and colors represent, but that's exactly what we deal with up there(even single-propeller folk like me).
I highly doubt the iPad will be much of a hindrance to that. What I fear the most is:
1) Pilots who rely solely on an iPad and forget to charge it, leaving them without the information needed when the battery goes(assuming they also don't have an alternate power source to charge the iPad).
2). The brightness(adjustable, of course) interfering with night vision. Lit items(instrument panel) are kept to a minimum in the flight deck because of the constant need to be able to keep a watch on other airplanes. Of course, pilots do need to turn on a light to read the plates when it comes time to land, but wise pilots will carry a soft light for reading the plates. Not sure how the iPad light affects it.
If I owned an iPad, I would definitely be interested in this app.
 Pilots who do this, without having any alternative source available in the flight deck are heavily frowned upon.
On #1, I've heard talk of having a sort of dock + external GPS feeding into the iPad, I doubt dead batteries are going to be a huge problem. I've flown primarily with a handheld, battery powered radio and that's never been a problem, though the batteries last longer.
And for what it's worth, the type can be really small on paper charts. A resizable view is a giant win, there.
Another solution might be to simply dim the display and enable a "red only mode" in the app, similar to Star Walk. There might still be some white light bleeding through the LCD, but it should be quite small.