half swording is not nearly as effective as a flail and it will never be B)
A flail might be effective, but you know what you have to do in order to get it on it's way?
Get it moving.
You know what you can to do with a half-sworded sword?
Get out of the way when the flail is swung.
On top of that, using the guard opens up a whole new world of hooking and grappling. Likewise, the length of a sword can also effectively give the used a warhammer when half-swording, if the blade is long enough.