Flying indoors is an advance flight move. It's not the drone that matters, it's the operator. So the question is not the P3 vs the P4. The question is if you have the flying skills to fly indoors.
I have flown indoors. All in all not bad when you have the space. I was wondering if the positioning sensors keep the P4 more stable for video production? Seems you can be less stable for pics than video.
I have flown indoors with the P4P. It was an empty building that was just being built. I had obstacle avoidance turned off, but the rest of my sensors were active. It was a metal building.