What do bump bands actually do? Are they worth buying?

[MamaG]

Am on 3rd pg and starting to peep a bit between trousers and tops. Not a good look in the office really

Do the bump band t hings stay in place, or roll up/down

Some boring coloured boob tubes in Primark now £1. At least in the one near my work. Exiting colours not reduced, but not pricey.