1 you're saying it's more effective to better advertise to a...

1 you're saying it's more effective to better advertise to a smaller market at one location than it is to advertise to a broader market at multiple locations.
1b I can't think of a logical reason to travel to a McDonalds 3 hours drive from here, when there is one now open just down the road.

2 you're comparing food, something everyone consumes, and do so on a daily basis, to a niche criteria of people diagnosed with breast cancer, who would be willing to voluntarily commit to a clinical trial, something that MAY come with side effects.
2b can't remember being overly fond of the idea of ordering food after getting food poisoning.

3 you're talking about a non-intrusive alternative means to detect ANY cancer from simply consuming food. This study is a test to confirm that in fact the nanoparticles cling to existing cancer cells in diagnosed patients.
3b This is not a burger that simply passes through you that you can get at the drive-thru window.