1h Flails are good vs humans, ancient dead and gobbos.
100% head hit + duelist’s arpen + cripling strikes = guaranteed neuted enemy with just 1 action, as “severe concussion” effect makes enemy counter productive for its own side.
Best case is OHK. Skellies and “regular” humans do OHK quite often, provided, you stack arpen.
Only donwside is a possible min roll on damage.
Flails are good vs orcs w/o head gear for the same reason.
On other hand Flails are terrible vs armored orcs, use hammers for that.