How well do teeth whitening trays from the store work?

I want to get the teeth whitening trays from the store. Do they work? How long do they take to work?

Is laser teeth whitening better at making the teeth white as compared to the trays the dentists give?

I had the trays once but they didnt make the entire tooth white, as if the product didnt cover the entire tooth, it wasnt uniform. will the laser (i think its laser), the one time whitening be better at making the teeth all white?