I don't understand why everyone thinks scrambler is useless. No, scratch that, I don't understand why no one thinks. Yes, in regular play it can be a telling sign of an enemy approach, but not to snipers who have their eyes on the scope. Also, it delays claymores. Is that not useful to you? I mean, fewer people use them now since you have to choose them over grenades, but try to tell me that you've never been killed trying to take out a sniper that way. And don't even try to convince me that you don't try to run around, guns blazing in hopes of getting kills without actual plans of how besides, see man, pull trigger.
Have you ever played hardcore? You know the radar only appears when you press start, so scrambler doesn't give you away unless they just watch the radar, and then they'll just have the menu screen up and won't see you coming anyway. Additionally, it delays claymore explosions, and I can assure you that hardcore players definitely use claymores. Ooh, search and destroy is another good one. I bet getting that last kill and going to defuse the bomb only to get killed by a claymore is kind of irritating.
I know this can be substituted for sitrep, but sitrep doesn't protect you from the explosions. Just because you don't know how to use it doesn't make it bad. If that were the case, then condoms must be horrible things(har har). Seriously though, scrambler is useful in the right situations, you just have to learn what those situations are.
Oh, and, um...hardline is dumb. I understand it and all, but most players can substitute needing one less kill with, well, getting one more kill. But, I can see why it would be useful to those who have trouble getting that one extra kill, so I can't say that hardline is useless.