This paper presents the findings from an evaluation of a Brain Computer Interface (BCI) with a group of people without brain injury and end users with acquired brain injury. The system held a number of applications to enable communication, web browsing, smart home control and cognitive rehabilitation. Participants engaged in a three-session cycle of testing and completed usability questionnaires within the user centred design approach adopted. The average accuracy score for the people without brain injury was 82.6% (±4.7) with the cognitive rehabilitation reporting the highest response rate. End users recorded an average accuracy score of 74% (±11.5), with the speller logging the highest accuracy score. The findings outline the importance of engaging with end users to identify the current functionality and usability of such systems in order to move them closer towards a marketable product used in a domestic environment.