It may be imagined that the length of the two-handed falx allowed it to be wielded with great force, the point piercing helmets and the blade splitting shields – it was said to be capable of splitting a shield in two at a single blow. Alternatively, it might have been used as a hook, pulling away shields and cutting at vulnerable limbs, or striking the edge of a strong shield. The inward curving point was still able to pierce the armour or flesh of the target behind the shield, rendering even the most reinforced shields much less effective against a falx wielder.
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Marcus Cornelius Fronto described the large gaping wounds that a falx inflicted, and experiments have shown that a blow from a falx easily penetrated the Romans’ lorica segmentata, enough to incapacitate or kill a majority of opponents. These experiments also show that the falx was most efficient when targeting the head, shoulders, legs and especially the right (sword) arm, which was generally exposed. A legionary who had lost the use of his right arm became a serious liability to his unit in battle.
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At the time of the Dacian wars, producing a long, sharp blade was technically challenging.[citation needed] As such, it might be that the larger two-handed falx was a high-status weapon and used only by the best warriors.[citation needed]

https://en.wikipedia.org/wiki/Falx