Stop overthinking it. Any seat in the 100s that’s not behind the stage is a win. You’ll have a great time, even if you’re in row BB of the upper balcony.
The real secret? The O2 is so well-designed that there isn’t a truly bad seat. Except the one behind a pillar. And the pillar seats? They exist. Look for “restricted view” warnings.
So buy the ticket, get a overpriced hot dog, and just enjoy the show. You’ll be fine. And if you see me in Block 111, wave. I’ll be the one not standing up, sipping a warm beer, and grinning like an idiot.