Love these pens
I have been very suspicious of whitening products as they either do not work/or work and harm your gums and teeth - and/or make you look like a freak. But these pens are great! You have to turn them quite a few times to make them work, but after that, the gel comes out easily. It doesn't taste 'dangerous' or acidic but 'clean' and it works - and I haven't even used my first pen more than 5 days but feel I can already see results. I am not quite sure if its best to brush your teeth afterwards, but I do, and I really like the extra clean feeling (and I love to brush my teeth).