Patients ask all the time about Crest's white strips. They are surprised when I recommend them. Most because they expect me to want to sell our office version but if an over the counter product meets your needs then by all means, more power to you! Save a dolla!
Any over the counter whitening product will be slightly less potent then a dentist dispensed product. That's perfectly fine depending on the level of white you want to achieve.
Teeth generally have two types of color to them. And they are not all white. They can have yellow hues or grey hues. I find grey hues on teeth make the teeth harder to whiten because the pigment usually comes from antibiotic use at a young age. They do unfortunately require more potent whitening agents. Yellow hues can be tackled much more easily and for this an over the counter product is great.
Personally I like the white strips. They are easy to use and you see results. Many patients say the top teeth lighten much better than the bottom and this is true of all whitening. I find it more so with the strips because our saliva loosens the strip and the peroxide washes our more quickly. I tell patients that you can just take a couple nights off from bleaching the upper teeth and focus more nights on the lower. With this recommendation they usually see a result closer to what they are looking for.
Whitening concerns are real concerns. Don't be shy and be sure to ask about your level of whiteness and your whitening potential at your next visit!