After the first normal cleaning head for my Oral-B rechargeable toothbrush wore out, I decided to try one of these whitening heads. They consist of a circle of quite-hard bristles surrounding a small plastic cap which is supposed to whiten the teeth.
These brush heads are supposed to clean the teeth as well as whiten, but the brochure that came with my original toothbrush recommended using a normal brush head first, then switching to the whitening head for one minute afterwards. This seems like an incredible faff and a waste of time, so I decided to just use the whitening head alone. I found that it cleaned reasonably well, but was not perhaps quite so good at cleaning in between the teeth as my regular brush head.
I did, however, notice an immediate change in whiteness. Whilst this isn't going to affect your teeth the way a whitening treatment would, and the difference is only likely to be small, I can confirm that there definitely is a difference, and the head helped with staining straight away. If your teeth are yellowed then you will need more than this to make them white again, but I would still recommend you try the heads as a little difference is better than none.
I should mention that I don't find these brush heads terribly comfortable. They feel slightly hard (verging on painful) on the gums, which I guess is probably due to the plastic circle. Therefore, if you have quite sensitive gums, I would probably suggest giving these a miss.