I thought I would like this whitening kit. I found it very hard to use. Sent back.I have been smoking a pack a day for last 15 years. After quitting (or significantly reducing to be more accurate) smoking, I realized how disgusting and yellow-stained my teeth were. I tried those teeth whitening stuffs from drug stores, but they were expensive and didn't work out that well.But this product, as far as I can tell, completely transformed my teeth into beautiful white color in less then 2 months. To be honest, I didn't expect too much from it. But I was disciplined enough to do this 2 or 3 times a week for 30 min each session using ample gels on both top and bottom teeth and cover them with mouth pieces that came with it. Here is one useful tip... You will have lots of saliva welled up during the treatment, so you might want to crumble a clean tissue paper and put it in your mouth to soak up the saliva which otherwise might dilute the gel... Except for a few times when lots of gel got into my gum, it was never hurting too much and I liked the taste and feel during and after the treatment, so I kept on doing it for about a month and half (and continuing) And I swear that when I look into the mirror in the bathroom, the tone of my teeth is more akin to that of the while towel hanging on the rack than to the yellowish marble wall of my bathroom. I asked my wife about it, and she is so impressed by it and started using it as well.I don't know if this will have any long-term side effect on teeth or my teeth will start turning back to the old color if I stop using it, but for now, I really don't care and I am just glad that I can smile confidently again and convinced that this kit really does whiten your teeth.I have been using this product for awhile now and it does in fact work great. I am seeing most definitely a whiter smile after a very short time. Thank you very much for that. After only a few days however the gels have become crystallized enough that I can hardly get the gel out of the tubes. This is a great product and I would like to continue to use it but am not able to. I would love to give this a 5 star rating if you can help me with this issue. Thank you also for the fast delivery time.I'm not to sure why other reviews are negative about this teeth whitening product. I can promise you that I used it 2 times 15 minutes each and I saw a differenece. I have tried so many over the counter products only to end up with $$$$$ spent and extremely sensitive teeth. I use the Watts whtening and then the green gel that you leave on your teeth and I my teeth, other than looking whiter would never know I used a whitening product. I am a smoker of about 30 years and I drink coffee a few times a day so the teeth either need to be whitened or removed. My smile was awfull. Now I can smile and I feel prettier. You women out there know what I am talking about. It helped me with confidnce issue and so on. Try it. I got the starter kit and I don't see running out any time in the near future.Very happy with this product. Use it about once a month to maintain the whiteness. Becase it is so strong, it does cause some tingling of the gums when it comes in contact with them, which is pretty much unavoidable even with the custom trays. The tingling lasts about 10 minutes out of 60 minutes that I use the gel. The custom trays work very well, but I ruined one of my first one by going just one second over the recommended time dipping in microwaved water. It is really true that they will curl up into a plastic ball.Affordable AND it actually works. I got the mouthpiece that lights up and I see a big difference every time! No more yellow smokers teeth! Yay!I whiten my teeth normally with crest white strips, colgate whitening tooth paste and whitening mouth wash. I think these will work great if you don't normally whiten your teeth. Since my teeth are already fairly white, the effect wasn't as good as my friend has (who doesn't normally whiten her teeth.) She ordered the same product and had immediate results. Also, for the price, it's worth a shot !good product, works well, but it's messy