This whitening kit was a complete surprise. Its signature ampoules (little pockets filled with gel that you mix and rub on your teeth) seemed like a gimmick compared to the strips we were all used to. But once we tried them out, we were sold. The Go Smile Double Action 6-Day treatment whitened our testers’ teeth an average of three shades — among the most of any product we tested — in just six days. Pretty speedy, considering the average time until full results for the products we tested was 13 days.

The gel was quick to apply and really wearable — you could whiten during the course of a day, which was a major bonus compared to messy trays or strips that, for better or worse, end up making you drool. One tester remarked, “It was super easy to apply after brushing my teeth. It was a quick habit to form.”

We also liked that sensitivity was minimal. Although Go Smile won’t disclose the exact percentage of peroxide it uses, it does confirm that it’s less than the ADA-approved 10 percent. Plus, the paint-on approach meant we were more in control of how much of the whitener got on our gums than having to manipulate and place one-size-fits-all strips.

Crest Whitestrips is a veteran in this space; it began advertising over-the-counter teeth whitening to the masses all the way back in 2001. We had high expectations for such a household name — and because of its 10 percent hydrogen peroxide levels, the maximum amount recommended by the ADA.

Crest delivered well enough. Our testers were all pleased with the look of their teeth after 20 days, but their teeth only whitened an average of 1.5 shades. Could it be because their teeth were already pretty white to begin with? Sure. An avid fan base, plus more than 800 4.5-star reviews on Crest.com and nearly 5,000 4.3-star reviews on Amazon, helps prove that more impressive results are common.

Crest makes a lot of lofty claims about its Whitestrips, not all of which pan out. Its website says you can drink water while wearing them — but one gulp turned our water into a whitening gel cocktail. No thanks.

Crest also says these strips grant results that last up to 12 months, which means you can do this whitening regimen just once per year; we didn’t have a full year to test this out, but on its FAQ page, Crest admits that, “The length of time your teeth will stay whiter is influenced by several factors, including how often you drink coffee, tea, dark colas, red wine, or smoke.” (Right. The weight you lost on a month-long diet will also stay off if you don’t eat carbs, sugar, or alcohol.)

But that stuff is just marketing. The only real downside was two of our testers reported uncomfortable gums while wearing Crest 3D White Luxe Professional Effects Whitestrips, again probably due to the high hydrogen peroxide content. Gum sensitivity occurs when the whitening gel directly interacts with your gums — this can happen if you apply the strips imprecisely or too high up on your teeth.

Tooth sensitivity, on the other hand, is highly subjective from one patient to another. If your pearly whites are prone to pain, we suggest Crest 3D White Whitestrips Gentle Routine.

Crest’s Gentle Routine strips have a lower concentration of hydrogen peroxide (only 3–7 percent) and you wear them for five minutes per day as opposed to 30. None of our testers experienced any sensitivity throughout their four-week testing period, but all reported some level of whitening and an appreciation for the lesser time commitment. “I put them on every night before I started my bedtime routine,” one explained. “By the time I was finished washing my face and applying moisturizer, I could remove the strips and go to bed. So easy!”

That said, it takes 28 days to see full results with the Gentle Routine — a full week longer than Luxe Professional Effects, which is something to keep in mind if you’re whitening for an upcoming event.

These teeth whitening strips punched above their weight. A 14-day supply of 28 strips will set you back just $12.43 on Amazon — that’s around $40 cheaper than a 20-day supply of Crest 3D White Luxe Professional Effects Whitestrips, and less than half the average $27 of all our testing products.

Our testers experienced little-to-no sensitivity (the levels of peroxide are at 6 percent with these guys) and an average whiteness increase of two to three shades — even more than our Crest 3D testers, although that has as much to do with our testers teeth than the strips themselves. Like the Crest 3D Luxe strips, you have to wear them for 30 minutes per day.

Downsides: one tester didn’t like that the gel seemed to stick to her teeth even after she removed the strips and rinsed with water. These guys may require a quick toothbrush scrub before you’re ready to go about your day.

Whitening pens bring out the skeptic in us all. As one tester puts it, “I expected to hate this thing. It seemed cheap and like it wasn’t going to work, but I like the way my teeth look. And it was truly convenient.” Start to finish, whitening takes about 30 seconds: twist the end to release the serum and paint it on twice daily for seven days. (Again, Go Smile wouldn’t say how much peroxide is inside, just that it’s less than 10 percent.) Both of our testers brightened their smiles by a shade in just a week. Not standout results, but not nothing either.

Theoretically, this little guy is so discreet you could whiten anywhere — in the office bathroom on a quick break or even stopped at a red light. “You can paint it on and then go about your day; no need to brush your teeth again or take off strips. There’s nothing to even throw in the trash!” one tester said.

Several recent Amazon reviewers have dinged the product for crappy manufacturing, claiming they couldn’t get the gel out no matter how many times they twisted the pen. Neither of our testers reported this, but, unfortunately, if it does happen to you, you may be out of luck. If you order the product over the phone via GoSmile, you can take advantage of the GoSmile return policy: return the pen with its unused materials up to 45 days after the purchase for a full refund or exchange. But if you order via Amazon, you’re subject to their return policy: if you open the pen and it doesn’t work, you’re stuck with it.