I'm using an iPad Air 2 to connect to an iPhone 5s.
Perhaps the issues are with the 8.1 iOS but it needs some work.
Pros - very easy install, I tested connecting via WiFi and bluetooth - in both cases the devices found each other. Bluetooth is a nice touch for when WiFi is not around.
Switching between front & rear cameras worked.
Now, the Cons -
Repeatedly, the app dropped the connection, forcing me to reconnect, which means going back and forth to "accept". This was right after taking a picture, and going back to look at a photo (which is necessary for reasons described below) dropped the connection.
The first picture I took worked, looked fine. However, if the app did not drop the connection then each subsequent picture was just a black square. I've never seen anything like that. Picture 1, fine, picture 2, just a "lump of coal".
There are no zoom controls or anything like camera or flash controls.
It's an interesting concept, and could be useful for many projects, but the dropping & "lump of coal" issues make this pretty close to useless.
I hope the developer puts some work in this, as this could be a nice utility.