The haft with a long chain and ball on the end is fantasy. However, I fought with one for a couple of years as a combat actor/choreographer and ren-faire reenactor and would say that the flail is a duelist's weapon only. And in a duel its chief function is to remove your opponent's shield.

A well placed flail strike will go around the guard of your opponent and potentially break fingers, hand, wrist, or arm.

You can also try to use it to disarm their primary weapon but it's less reliable in this regard as it becomes a tug of war strength contest.

Use your flail to break their hand and make them drop their shield and then drop the flail and draw your side sword or whatever else you happen to have.

Too slow and clumsy of a weapon to fight against a group or near allies.