it is main stage, but this year with the long stage queing will be much nicer. As with the multi shows attended last tour, red zone was let in same time as the GA and you had option to que on the rail . I did both with red zone and found red zone access and ease to roam without pushing against you was a great thing. Plus, the wife is vertically challenged and will enjoy the show more.
I do know though of all the 50+ u2 shows I have seen, GA is the best no matter where you stand. Nothing like it the the seats cannot come close to.
Enjoy, do not worry about the red zone area, you are