A key challenge in legal knowledge representation is the construction of formal knowledge bases. Such knowledge bases then allow for various applications such as legal reasoning. In recent years, several approaches have be developed in order to create such knowledge bases. A major goal of all the approaches is to be usable by legal experts. While some of these approaches have been tested with legal experts, there is no experiment which compares them with the same control group. In this article we define the main user interfaces for legal formalization and various required criteria. We then design an experiment intended to compare the different approaches according to the defined criteria.