I'm sure you can't do much wrong with the GoPro, it is the most common choice around... there must be a reason for it.
Cannot really comment on the mic input since I use a small separate audio recorder and combine both tracks later. I never had a problem with that. The camera mic delivers the background sound and the recorder adds ATC.
By the way:
A recent NVFR flight filmed with my VIO. The sky was indeed looking unusually nice that day but admittedly not that greenish... I'm not exactly sure yet why it turned out to be rather greenish than blue but I guess it was the white balance... beside that i'm really happy with the (very) low light performance. The pictures is crisp (until it got into youtube's hands...) and surprisingly low on noise!