The thread was taken down when I tried to post.
Here are my comments
The maximum % peroxide bleach in the uk is 6%. Years ago when my then dentist made me trays I could get 21% bleach from my dentist or online.
I am now using top up bleach from my dentist and the law has changed to a max 6%.
If you whiten your teeth you ought to have them checked over by the dentist first. You need your gums checking and also your fillings as trays (not strips) cover the sides as well as the front of teeth.