Pat,
it was designed to be used in conjunction with chemical bombs, to indicate wind direction. Nobody had chemical bombs (other than some smoke and incendiary) in WWI. The Italians began development of their bombs in the early 1920s, using some very small models in Libya.
Italy is identified in numerous sources as having used much larger chemical bombs against Ethiopia, in conflict running from the mid-1930s into early WWII. While a number of small to mid-sized Italian bombs and submunitions have been found in Ethiopia, as well as several thousand projectiles, none have yet been identified as CW, and no Vento bombs.
Likewise a number of chemical filled bombs have been found in different areas in Italy (and destroyed), but I have never seen a Vento bomb at one of the sites or been told of one being discovered "in the wild".