I've read on these boards that you can also use those plastic tie straps (the ones you see the police use as handcuffs). If security needs to get into your luggage, they can just cut those and replace them after they're done.
Of course it's not a "lock", but as you all say, if someone shady wants to get in, they'll get in no matter what.
I just thought they were a pretty good idea when I read about this. You can at least have a small amount of security knowing that your bags are somewhat secure instead of knowingly having them sitting open. I've put a bunch of them away for our trip. And if they've been cut, I'll know
someone has been in my bag, instead of just leaving it open. Doesn't solve anything

, I'll just know.