I whiten my teeth about twice a week because I drink so much coffee.
Right now I'm trying those Brite Teeth Pro pens and they seem to be doing ok.
I'm not using them to go whiter though, just to keep my current shade.
I bought mine off Ebay for i think, 2.99 for 2 boxes of 2?
Don't go through the company, major ripoff otherwise.
My favorite is the Plus White 5 Minute something or other, I got it at Walmart for dirt cheap and it was the first I ever used, but it definitely worked a few shades.
It came with a ton of gel and it covers more teeth than the strips.
On that note, I've also used the Crest 3D strips, which worked pretty alright but I'd much rather use the quick tray.
I've never used Rembrandt, but honestly, i'm pretty sure all these have the same damn ingredients.
I'm no expert but I dont think you can go more than a few shades lighter without actually going to a dentist and having some crazy chemical light shit done either.
Although I know on Ebay you can buy the lights...
Cautionary tale, I go to the dentist every month because I now have to have Fluoride treatments and I use a prescription toothpaste
I do not know if my OCD whitening had anything to do with it haha