It's great for terrorist attacks, but not really a good weapon.
It would be more effective than chemical weapons in that it is more persistent, has delayed action and can be spread person to person or through animal vectors. This means it would be possible to deploy it more discretely and that it requires greater effort to contain. You're right that it is a better weapon for a terrorist attack or asymmetric warfare. It would still make a good weapon for creating an undue amount of stress on a region's medical capacity, if enough people were infected then a significant amount of antibiotics would initially be used attempting to treat them and a lot of resources would go to containing the spread, quarantining the infected or potential exposures and providing supportive care to a lot of people that would inevitably die very miserable deaths.