Do you watch the drone or the screen when flying with drone within sight?  I’m thinking of adding an iPad mini 4 to better see the screen.

always both

You need to be able to see the drone at anytime but you will also use the screen to navigate and line up shots so yep, both.

Good idea to add the bigger screen if that works best for you. Yes, I usually review the screen and drone while in flight. At one point I'd thought about getting ipad mini but decided against it only because the iPhone 7 Plus was just right for me.

I watch both.  I like to know where my drone is in relation to me and I like to "see" what my drone is seeing.

Everyone seems to find their own setup, myself I use an iPad full size.. much easier to see what you are shooting.

As a beginner, I suggest you maintaining eye contact with your drone when flying out, just to get the sense of your orientation. Once you feel more comfortable, you can use your screen (iPad etc) as your visual. Still, FAA says that you should always maintain visual with your drone but when it's a bit far away, it's a challenge.

AS always you need to maintain LOS. How you do it it is entirely up to you and your common sense!

I just bought an ipad mini 4 last week and I can tell it works much better than a smartphone.
Size does matter, at least in this case.

And I mainly look at the screen (except taking off and landing) as I usually fly my drone over 6000 feet away.
I  like flying to the open sea so I think it's not that dangerous and there is no law to maintain LOS in Hong Kong.

Both I use an iPad mini.

Hi, just for the mobile device that you refer to, iPad mini 4 can fully support running DJI GO 4, no worries.
For my personal experience, I would also look on both, and I will also need to look into the mobile device so I would know which angle will be a great one.

Depends on where you are flying, constantly check both is best.

Always both ......  it will become more natural the more you fly.  

Thanks to all!

I watch both. My screen is a normal-sized Android. One of the things I notice (or don't notice) is the details I missed while flying. When I get back to the computer and watch on the screen I see all sorts of interesting stuff I missed while flying. Stuff I would have liked to have concentrated on. So some day I think I would like to put a bigger screen on just for that purpose.

This brings up a nagging question for me... I have an MPP that I think has something like a 4 KM range? Something like that. Yet I keep hearing I should never let the drone get out of sight. I watch videos here and on YT and I see drones flying all around the environment obviously out of sight of the operator. I can't tell if this is some federal (US) regulation, advice from experience to a new user, or just a case of having a 250 MPH car in a 65 MPH country. What good is 4 KM if you're not supposed to fly past a couple hundred yards (57 year old eyes).

It's like I got into this hobby or activity only to find out that I might be breaking a law if my drone flies out of sight. If I can only fly as far as I can see then the only advantage a drone has over a phone's camera is angle.

Kev