Great option . Given that you already tried the otc whitening products without much success, professional teeth whitening is the next logical step. If you are ok with the cost and are given the right expectations by your dentist, there are actually no cons. The main advantage is that the whole process is done under the doctor's supervision, so the safe and effective outcome is assured. Good luck!
Pros/cons. Pros: best chance to get the most white, custom fit for you, safe, works well cons: cost, increased sensitivity (usually temporary), no guaruntee what shade you will get to. Yellow bleaches better than brown/grey.
Better results. Con; more expensive, but worth it if you really want a more lasting whitening. Over the counter systems generally not strong enough chemicals to make a significant difference.