They're quite a strong faction if they emerge and always seem to go first for the French rather than the HRE in my experience. They're dealt with in much the same way you'd deal with any other heavy pole arms/spears/pikes unit. Wear down with crossbow/arbalest/longbow fire, then charge heavy infantry such as CMAA, followed by a charge to the flank with devent cavalry. They're only dangerous if you do something stupid like charging them head on with any cavalry.