I was impressed by Lightroom Mobile on my new iPhone 7 plus, but it all ended with one important feature missing.
Using the touchscreen for shutter release is really awkward, so for years all iOS camera apps allow you to take a photo by pressing the volume button. This way you have a completely different, more stable grip on your phone, essentially you are using it like an regular camera.
For some reason this is missing in iOS Lightroom. Hopefully this will be adressed soon in an update. I'm really looking forward to use Lightroom as my default camera app, right now its not ready yet.
Also, the switch between wide and telephoto lens is very slow, with a noticeable pause. On the default camera app its instant. Not a deal breaker, but I'm wondering why this delay occurs.