Typical behavior would dictate that the offhand use function is only used when the main hand use function is not valid in the current situation. However, with this mod active, any special placement provided by it will override the mainhand use, such as when you're trying to use your bow, crossbow, or trident.

Fixed (I think?)! It should be in the next bugfix.

If you're holding a bow in your main hand and a block in your offhand, it will use the bow now, unless the bow has no ammo.