Once you enable Hi-Res NDI and Retina in settings, it looks halfway decent (those should be enabled by default, or at least you should be told that it will look like garbage until you do that). To those saying the audio doesn't work, I've discovered you cannot have your device in silent mode for it to work, unlike several other apps that show video or make noise.
It freezes and crashes quite a bit. I found any time I switched sources, it would either crash or freeze requiring a full close and re-open of the app. Though, half the time, when closing the app, it'll crash itself, meaning if I switch to another app for a second and come back, it'll have crashed and I'll need to select my source again and wait the sometimes 30, even up to 45 seconds for it to reconnect to my source, if it does at all.
I also find it randomly crashes, such as when getting a system-wide alert, or sometimes even when getting a notification from an app. Swiping down and opening control center (even just beginning to swipe down, by accident, and not opening it all the way) will also result in a crash, similar with pulling down to see your notifications in Notification Center.
It also requires a fairly new device to keep the stream going. The preceding thoughts were written based on my experience using it on my iPhone XS Max. When it tried it on my iPad Air 2 (admittedly an old device but it still holds up to other tasks and even some games quite well), the stream was very jerky and the audio cut out a lot, eventually causing the app to crash. It should be noted the two devices were in the same physical location, which is quite close to the Wi-Fi access point, and gets a very respectable amount of bandwidth in iPerf tests on both my phone and iPad. I have not tried wiring the iPad (or my phone for that matter) in with the USB-Ethernet adapter + lightning camera connection kit, but I'll give it a shot. I suspect it won't help the stuttering and jerkiness on the iPad, though.
Overall, I'm disappointed with this app and wish there were alternative apps available. The only reason I'm giving the app 2 stars is because it does actually receive and show NDI and audio (most of the time, anyways).
It's interesting, because I quite frequently use the Sienna NDI Monitor app on my Mac, along with a few of their other NDI tools (I actually prefer their NDI Monitor over NewTek's), and would have expected more from them in an iOS app.
The app is very much not worth the $9.99 I spent on this app.