You know what is sort of weird? Someone with Two Weapon Fighting and Knife Basics could wield a flail and a shield. They could take -2 on their attacks, attack with the flail and shield, then stab someone with a stiletto, while continuing to wield the flail and shield. If they have Flail Basics, too, this could become slightly surreal. In one round, they could attack with the flail and shield at -2, the stiletto at -2, then attack a flat-footed character with a flail at a total of -6.
Seems reasonable to me. You have a shield readied, a flail readied, and a knife readied. Use them in whatever combination you like. Opponent thinks he has your number... and then you leave a knife in his ribs he never even saw comming.
Oh, I'm not saying it's wrong, or overpowered, or unreasonable. Just... sort of weird.
And I can totally see it in a Jackie Chan/Legolas kind of way, where there are weapons, and there are foes, and sometimes they meet each other in sudden and deadly ways.