I said I'd do it. Now I've done it.

I downloaded the Burger King app to my iPhone, and drove to a McDonald's in Little Falls, New Jersey.

Then I ordered a 1-cent Whopper on the app--the first Burger King food I've ordered in many years.

I registered, filled in my credit card info--and just like that, my 1-cent Whopper was being prepared. The app even pulled up directions to the Burger King I now had to drive to, about a half mile away.

The whole thing is part of an ingenious campaign to get people to download a fast food app--something that's frankly better than what its competitors have come up with.

Sure, McDonald's tempted people by offering a Gold Card that could get you two free meals a week for 30 years. Starbucks is offering "free Starbucks for life."

But Burger King beat them both with this thing, called the Whopper Detour promotion.

It lets you order a Whopper for just $0.01, but requires you to do so from within one of 14,000 geo-fenced McDonald's restaurants in the United States. (Technically, you can sit in the parking lot as I did; you just have to get within 600 feet of a McDonald's before you order from Burger King.)

The promotion went live Tuesday morning. When I got my 1-cent Whopper in the afternoon, the woman behind the counter at Burger King said she'd been seeing people come in all day for one-penny burgers.

I think the whole thing's brilliant--even though I confess that I wound up eating two bites of my 1-cent Whopper and throwing the rest of it out. I just can't eat that stuff anymore. I'd say the same about McDonald's.

But setting aside the fact that I'm not exactly the target market for this thing, here's why it's so smart:

1. It's technically advanced.

It seems like every company is trying to get you to download their app, but this campaign uses a smart, unique feature. Geo-fencing isn't exactly new of course; Pokemon Go was what, three years ago? But this is the first app I've seen like this, and it made it a game. 

2. It trolls the competition.

Check out the promotional video at the end of this article. Burger King has some good trolls working in the marketing department. It's just creative and funny that they'd think to offer a discount, but require you to go to their main competitor to redeem it.

3. It enlists customers as allies.

This isn't just Burger King trolling McDonald's. It's Burger King recruiting thousands (I'd assume) of customers to do it with them. Everybody likes to be in on the joke--and they're getting pretty good media coverage out of it, too.

4. There's almost no wastage.

Part of why I love this is just out of respect that Burger King winds up getting people to download and activate their app almost for free. Yes, the Whopper is almost free, but when you factor in the drink and fries customers almost certainly buy, they're probably at break-even. Other companies are thrilled to get app downloads for a few dollars each; getting them for next to nothing is genius.

5. They make you activate.

Why charge a penny? Why not make the Whopper free? Because doing so means you don't just have to download and register the app; you also have to sign up with a credit card, which Burger King helpfully saves. Now, they can send you push notifications and maybe convince you to buy more food with one tap.

So good work, Burger King. I barely tried your burger and ultimately deleted your app.

But you convinced me to make a detour all over New Jersey in pursuit of a $4.88 discount on a sandwich I didn't want to begin with. That's pretty darn good marketing.