How so? Let's say I pay AT&T $30 for 3 GB. Then I pay Netflix $2 for 3 more GB. I use all 6 GB. I'm not getting charged twice.
But what about you? You only use 1 GB of data normally and another 1 GB for Netflix. You're already paying for 3 GB in total. Well then you shouldn't sign up for Netflix's little $2 deal. That's the better plan for this hypothetical you.
The only way this could be bad is if Netflix doesn't give you that choice and makes you pay that extra fee no matter what. But my god, that'd be stupid of Netflix, wouldn't it?
Go grab a balloon. Inflate it. All the way until if you put any more into it, it will pop. Now tie it off and put it on table in front of you. That's the total amount of bandwidth you and I pay for each month from AT&T to do with how we please.
Now squeeze that balloon so that 2/3 of it is on one side of your hand, the other 1/3 on the other. That 2/3 is the part you pay for that you actually used under a model like this one. The other 1/3 is the part that Netflix "subsidized" by charging you a little extra for the movie you want to watch. AT&T doesn't charge that 1/3 against your total usage (how nice of them) because they are getting paid a fee by Netflix for that 1/3.
But wait a minute. That whole balloon is your bandwidth. Its just that now you've paid a little bit more to Netflix to not count that 1/3 usage against your total monthly usage.
Now if your month-to-month usage stays the same...that is to say you don't use any more bandwidth with this program in place than you used to, then you just got charged twice for the same bandwidth. Once when you paid for it, a second time when you paid Netflix to buy it on your behalf from AT&T.
Do you think Netflix is going to charge less for that content because you are using their data plan? Nope, they'll charge you a premium. Do you think AT&T is going to discount your monthly fee because you used 1/3 less than you normally would have by using Netflix pre-paid data plan? Nope, they will just not throttle you that month.
In fringe cases, you could possibly go to lower-tiered data plans if you used this enough. Perhaps if AT&T did away with mandatory Tiered data plans for smartphones, and had you pay by the drink this could possibly end up being a savings to the consumer. But I'm sure they've run their own numbers and it will never be cheaper to pay by the GB than going with a tiered plan.
Squeezing the balloon is the nature of the industry, AT&T just happens to be more creative about it. That and they are like the house in Vegas and the house always, always wins.