Historically the two handed falx seem to have been worn without shield. The Dacian warriors on Tropaeum Traiani / Adamclisi monument have none with obvious two handed weapons. Four types of sickle weapons are shown. .
The weapons of Traian column had been made from metal and are mostly lost.
The Dacian shield was held by hand on the central grip, we know of no versions with slings to have the hand free. So a shield bearing warrior has to use the weapon with one hand. And then to drop the shield for two handed use.
The findings show falx weapons of different size. But we see also ordinary swords and battleaxes. And small “sabres”. The falx was a cutting arm with no stabbing option. Not ideal against a standing shield wall but brutally effective in open fight.
It would be stupid to give them to a large part of an army for open battle. But good for raids on columns and trains. The high cut opens the body to the stabbing gladius, As long as the Roman stayed cool he was superior.
The short one was called sica (sickle) ,see Valerius Maximus III,2.12.. The longer was the true falx.
Named ensis falcatus (Sicle sword) in Ovid Metamorphose and falx supina in Juvenal Satiriae. It was a weapon loved by grammar writers like Marcus Cornelius Fronto. With an emphasis on studying ancient writers in search of striking words.
For the Roman it was a Topos, to show the Barbarian Dacian with one, semi nude. So on Monument the Viewer knew at first glimpse: A Dacian.
.
