I am a fan of NDI. It already worked fine on my previous iPhone and now on my iPhone 12 Pro it works great too. But...
Two things. First it really really needs a camera stabilizer. Many other camera apps have that (like FilmicPro). I think the iPhone 12 is powerful enough to stabilize and encode the video at the same time. It might be getting a bit more delay, but than you should have the option to switch of and on.
Also i want to be able to switch camera’s. It has 3 cam’s, (0.5x, 1x, 2x) but it uses only the 1x cam (and selfie cam). Good, but being able to use the others would be even better.
And last, but not absolutely necessary, a other way to use the zoom. Instead of first ticking on the ‘weel’ and than use a finger on the screen to zoom I and out, and with doing that making the picture vibrate a bit, maybe use the volume controle or a Bluetooth thingy?
So it is a great NDI app for use as a extra cam in your (live) production, like making flash interviews, an extra eye for that impossible shot or just a selfie shot while doing your thing.
Bottom line: Get it, use it. But it also needs a serious update.