Can the Self-accounting feature be activated in every bundle?

In the paid bundles (Small, Medium, Large and Unlimited), a user with Backoffice accounting functions is included by default. 

An additional user with Back office accounting functions can be activated for €25 per user. In the bundle Small, however, this is not possible because only one user can be created there.

In the bundle Minimal and the Trial environment the feature Self-accounting is not available.