Are insoles good at preventing flat feet, stabilizing the heel and supporting the arch of the foot?

Helps with support: Insoles help with support, however there has not been a study showing that insoles prevent arches from falling.

If your feed need: Support, they are by nature unstable. It is all hereditary. It isn't about whether your feet are flat or not, it is about how stable they are. If unstable they need firm support--discipline, if you will--good orthotics, not too cushioned or flexible, would be best.