They come in several sizes and wingless and flightless as well.  Flightless is a better choice than wingless, as wingless can revert back to the flying.  You shouldn't have to worry about escapees, because the company will have secured them. They breed in the vials, but it's not recommended: they will over-crowed and die. Fill the cup up 1/4 full, maybe a little more, and this lasts about a month or so. If you use "Organix" remember to add the mold inhibitor.

Summary:
When buying fruit flies, choose the type of fruit fly you want, online. When buying them, get an extra order of fruit fly media (food), bedding and culture cups. When the box comes, remove the contents. If they are in small vials, put them in a freezer for a couple seconds, no more than ten, to slow them down a little, then pour them into a culture cup. Pour the fly food into a culture cup, adding the amount of water the package instructs you to. After assembling your culture cup, add the flies you bought/caught.