It's kind of been said, but I did want to reply to you Harmless Kittens:
It's not "banned" unless you're playing in one of those private matches for one of the competitive leagues. I can safely assume you are not and probably aren't interested in them.
So, there's nothing stopping you from using them. In general, the long-term players will give you a lot of crap for using them... and they have their good reasons. I have chosen not to use them, in order to 'keep the peace' and maintain a gentlemanly spirit in our small community. But, I see no real reason that YOU shouldn't feel free to equip them and go experimenting with them.
As for how useful they are (especially related to the general disgust folks have for them), it comes down to the same fact as everything else in Hawken; they are only as good as the players ability to use them to their full potential. You absolutely have to be really good at always having a third eye on your radar for them to provide you with a significant level of benefit. If you're already weak at always noticing what is on your radar, the Scanner item will still only benefit you when you do happen to look at radar.
What it does: It provides enhanced radar in a fixed diameter range that shows movement of opponents. Normal radar only shows opponents when they shoot, boost, jump or dodge. The Scanner shows them no matter what. (I cannot recall if it spoils the cloaking of Preds and/or Infiltrators). It also provides that same enhancement to any of your own teammates when they enter the Scanner's range.
I think it is the "provides radar enhancement to all teammates" part that really gets most people fired up... and that they call it a 'global wallhack'. I don't think it's nearly that bad - because it is not 3-D and only shows that info on the radar in the corner of your screen. It also makes a distinct enough sound that opponents usually eliminate it within moments of its being deployed (unless you're incredibly crafty or know all the spots where you can toss it inside of objects - which is more of an exploit).
Again, I don't use it to 'keep the peace'... but have also learned there are items which are ultimately more valuable to my success in-game.