I actually got the kit from my doctor to begin with, as I got the custom molded trays.
Within 2 weeks time of doing it for 45 min to a hour once in am and once in pm the shading on my teeth went from a 7 to a 2. The only problem I had I didn't put it in the exact spot on the bottom tray, therefore near my gumlines it is still yellow, however will do touch up and all will be good! Glad the touch-up kit is available via Amazon since the dentist is $200.
Yes when the bleach got onto my gums it did burn, but that is to do the high percentage of bleaching concontion that is used. After wiping it off, it never bothered me again.