I bought this kit a few months ago after trying the Crest Whitestrips with no results (although, granted, they were a couple of years expired). Anyway, seeing the great reviews for this whitening kit and the much higher whitening strength of the gel, I decided that for the price it was worth at least trying out.
One issue that I noticed a few reviewers had were with fitting the mouth guards. Although it can be a little bit tricky, this really isn't very difficult to do, and if you read the directions and do it exactly like it explains (practice first!), you shouldn't have much of a problem. First off, when the directions say no more than 3 seconds or so, it means it! Anything longer than that melts the tray so much that it folds and loses all shape. The top tray was easiest to do, and I fit it perfectly. But I did have a little more trouble with the bottom because it is more difficult to get the proper suction on the tray for it to fit right. BUT you can re-dip it in the water and do it again if you mess up!!! I re-dipped the bottom tray 4 - 5 times before I finally got it where it worked for me. It doesn't change it or hurt it at all by doing it several times, so if you mess up it's no big deal, just do it again. There's no need to throw it away and use the second pair. Also, the directions say that you do not need a perfect fit for the product to work, but the better the fit the better it will whiten. As I said, I had problems fitting the bottom tray, so it didn't fit to my teeth as well as the top tray did. But since the instructions said you don't need a perfect fit, I decided it would be ok and didn't worry about it. But after a few whitening sessions, I noticed my top teeth were getting much whiter than my bottom teeth and that they they didn't seem to be whitening much at all. So that's when I decided to try to remold the bottom tray and make it fit better. After several tries, I finally found that actually physically holding the tray tightly to my teeth worked best. At the same time, I also ran my fingers along the entire tray to make sure that it fit tight against my teeth. The tighter it is, the less saliva gets in and washes the gel off your teeth. For me, this was key! After I did it this way, my bottom teeth finally started to noticeably whiten.
Now on to actually applying the gel. First, I liked to dry my teeth off because I figured the gel would stick to my teeth better. And instead of putting the gel in the tray, I applied it directly to my teeth using the syringe and just spread it around on my teeth with the tip, which was quick and easy to do. I also found that it works best if you put a pretty decent coating of gel on each tooth, because saliva does seep in and start to wash it out. So if you put too thin of a coating, the saliva will wash it away pretty quickly and not give enough time to really whiten. Since the product comes with a big syringe of gel, you have more than enough to use and don't have to skimp. I used it for about a month and still have some gel leftover.
Granted this is only my second time to whiten my teeth, and I haven't really tried many of the other products available, but this kit worked amazingly well and everyone has commented on how white my teeth are and have even asked me what I used and where I got it. I used it a month before I got married, and one of the first things I noticed with my wedding pictures was how blindingly white my teeth looked, which is exactly what I wanted. I couldn't be more satisfied, and I would recommend this product to anyone!