I was looking at the Sengoku Period Samurai army list, and it allows Ashigaru units armed with arquebus and longbow to be equipped with a Pavese, which reduces movement.

However, the army list does not state the benefit that a Pavese gives to a unit. Since these are defensive screens, am I right in thinking that it would increase a unit's VBU by 1?

Many thanks

In Impetus they give a -1 to anything shooting at the archers behind. I presume it will be the same.

this is the rules for Pavise

Special Rule. Crossbowmen with Pavese nullify Impetus Bonus of mounted ememies and give a -1 malus on shooting if charged or shot at from front.

this is a special rule present in the lists (this is taken from Italian Communal list - Vol20) . Simply in Samurai list it has been forgotten, I will include in the next update.
The rule apply to all troops with Pavise, so in case of some other missings apply it.