Cash, credit or smartphone? Apple has promised that its Apple Pay service can revolutionize the way we shop, replacing the normal credit card swipe with a tap of the phone and a fingerprint scan. But we wanted to see if Apple Pay would work as promised by using it in a tough real-life situation: McDonald's during the lunch rush.

The fast food joint in question was in the food court at Arlington, Va.'s Pentagon Fashion Centre. With a tour group of middle schoolers in front of me and retail workers on half-hour lunch breaks in back, it was the ultimate test for a payment method that's supposed to cut down on time spent at the register.

It worked like a charm. I ordered two things off the dollar menu and was done paying by the time the cashier had repeated my order back to me. And with nothing to slide back into my wallet, I was able to move to the pickup counter so fast that the impatient man behind me hadn't yet figured out his order.

In the interest of being thorough, we also ran tests at a few other places. Participating stores list Apple Pay, which launched this week, as an option alongside accepted credit cards. Apple has said the process is simple: Consumers only need to load a credit or debit card into the Apple's wallet app called "Passbook" by entering the numbers or taking a picture of the card.  In general, we found the experience was indeed pretty easy, though it had some key limitations, particularly which cards you could choose (sorry, no Amazon card yet). And, ironically, Apple Pay wasn't great when it came to buying stuff through apps on your smartphone.

Apple Pay worked at the Apple Store, because, well, duh. Things also went smoothly at the Whole Foods in downtown D.C., apart from the fact that the cashier laughed when I plunked my enormous iPhone 6 Plus, a review unit on loan from AT&T, onto the card reader. Mild ridicule aside, it was just like using a credit card -- but, yes, slightly quicker.

Sometimes, it depends on who's behind the cash register. At Macy's, the cashier had never completed an Apple Pay transaction and asked sheepishly if she could pull out her training sheet. Once the transaction got going, however, the sale went without a hiccup. The cashier even commented on how quickly it went, saying it would likely save her time in the coming holiday season.

Returning items was also very easy. I didn't need to pull out my phone or my credit card. Armed with just the receipt and the scarf I'd just bought on a lower floor, the Macy's customer service counter was able to process my return and give me my money back without a hitch.

Apple Pay is not going to work in every case. CVS, which was not an Apple Pay launch partner, has card readers equipped with near-field communication chips -- the technology behind Apple Pay and other similar services. But Apple Pay didn't work at the self-serve register. The phone beeped to let me know the chip had been read correctly, but it didn't actually trigger anything on the screen or charge on my card; I still had to swipe to pay.

Also, it won't work with every card. Of the plastic I carry in my wallet, only the Visa debit card from my bank worked with Apple Pay. Some branded cards -- department store cards, airline cards, etc. -- aren't yet supported. The same was true of my corporate American Express card. Amazon said its branded Chase Visa credit card will eventually support Apple Pay, but hasn't yet set a timeline.

But the real hole in the service comes when you try to buy things through apps on a smartphone (Apple Pay doesn't work on Web browsers since it requires a fingerprint scan). It's all well and good to pay for Apple Store and iTunes items via Apple Pay, but the company still has a fairly limited range of apps that accept the service. And the implementation isn't always quite right. At Target, for example, you can only buy items one at a time using Apple Pay. But if you put multiple things in your cart, Apple Pay isn't an option. Choosing Apple Pay for Uber, meanwhile, actually adds a step because, rather than hitting a single button, you have to verify your fingerprint when you pay.

The experience itself is similar to other phones that have enabled users to pay by tapping, though the addition of the fingerprint scan does lend a certain air of security without adding too much time. Like its predecessors, it needs wider support to graduate from novelty to necessity -- or at the very least, more consistent support before we can say the wallet of the future has arrived.

Still, Apple Pay's convenience may still surprise you. Walking by a vending machine at the mall, I noticed the card reader had the symbol that indicated it worked with NFC-enabled devices. On a whim, I tapped the phone against the machine and my thumb against the fingerprint reader. Three seconds later, I walked away with a cold Coke and a certain feeling of giddy satisfaction.