I've been using Go Smile ampoules on and off since they came out in 2002. These "boosters" along with the "Super White" or whitening pens have always worked to whiten my teeth.I've seen complaints about them not whitening enough. It's important to keep in mind that it matters what your starting point is: if your teeth, like mine, are already fairly white, your result is going to be more subtle. And if you want your teeth whitened, say, 7 shades, go to a dentist to see if you're a candidate for a professional treatment. Considering how much that would cost, I think these give me plenty of bang for the buck. ( I don't have sensitive gums so that isn't an issue I need to worry about.)I'm really writing this review because of all the people complaining that they can't figure out how to use it, that nothing comes out. This is not the fault of the product: this is operator error. The directions clearly state that you need to pull the ampoule out of the cardboard tube, flip it so the brush end is sticking out, then squeeze the tube to crack the ampoule and push the serum through the brush. This keeps the product fresh and active. The design is ingenious, in my opinion.Just working well isn't enough: it has to be convenient. I don't know of any more convenient method unless maybe an elf comes in and cleans your teeth while you sleep. On second thought, that would be creepy. Unless it's Hermey; that would be great. (Yes, I just googled the spelling of his name.) I can't stand white strips. I've used Glo Science, which is excellent, but just not, you guessed it, convenient.So for every obsessive who will spend hours poring over Amazon reviews, I say this: If you're looking for something portable and easy to use, that will make your smile somewhat brighter and momentarily make your mask breath minty, if we're still wearing them when you're reading this, just stop scrolling and buy this and go do something more fun. You can always return it, right?Very good product and I received my order quickly!!! Actually sooner than expected -- very pleased!!!!!Just break the glass at the half green on with your thumb and finger (kind like a hard pinch) and whichever you’re comfortable with either left or right to smash! Then tilt your head up and have the go smile smash glass white down with your teeth. It helps if you squeeze the container occasionally when brushing your teeth to ensure the liquid comes out.Easy to use, no sensitivity issues and it works!!!Did formula change? It seems soDon't seem like the real product and doesn't whiten like what I expected or bought on a cruise a few years agoI find these to be the perfect refresh. I have used for years, no sensitivity or burning.Great