Yes they do work on expanding the size of your breasts though keep in mind that there are a number of restrictions to these devices. The main limitation is that these devices require a significant dedication in your time before you can see any results.
Don’t try for huge breasts right away and don’t over do it. Don’t pump so hard that your boobs turn purple! Go slow and steady and over time you will see results.
If you want quick, permanent breast growth, breast suction pumps are not for you.
If you are patient you can slowly increase your cup size, Pumping coupled with wearing a good bust shaper will definitely increase your bust line.