That was my issue, I realized I needed a backpack when carrying my P4 on its shell case (the grey one that comes with it) last week when I went hiking, it was a really easy hiking, no more than 15 mins and I was really arm tired for holding that big grey box...
I have a Protactic 450AW that I carry my camera stuff in, but the drone fits really tight, I am afraid it might break something, plus with this bag it's the drone OR the camera, with the droneguard it can be both