Abstract-Feature models are considered a reference in the majority of Software Product Line (SPL) methods. There are several different feature model notations to represent requirements of an SPL, at a higher or lower level of abstraction. Some notations present properties to distinguish functional, conceptual and non-functional features of an SPL. Non-functional requirements, especially those that involve the construction of user interfaces (UI), are usually not represented in the feature models, since the user interfaces are often created manually for each product. In this paper we present an experimental study performed in order to evaluate the effort required to, as well as the benefits and drawbacks of representing UI elements during the feature modeling of a Financial SPL. To this end, we applied the Odyssey-Fex and UI-Odyssey-Fex notations to design feature models from the perspective of Domain Engineers in the context of undergraduates, M.Sc. and Ph.D. students and software engineers with some expertise in SPL. Our results indicate that the effort to use the notations are similar, but the use of the UIOdyssey-Fex notation provides a better representativeness of UI elements.