Hi,
I've attended 2 I&E concerts so far. If you're seated directly behind the main stage, there'll be 3 disadvantages; firstly you won't see the band during the mid section, where the disappear into a screen in the middle of the stage. Secondly you won't be able to see the screens properly, which are a major part of the show. Thirdly. the band go the far end "E" part of the stage during the 3rd section of the show. If you can try and get better seats. Having said that, it's a U2 concert, so the atmosphere in any section is electric. Good Luck!