This paper presents a case study where a cost management project was implemented using action research methodology at two Finnish organizations working in a purchaser–provider relationship. While the study demonstrates the efficiency-seeking motive behind the implementation of the management accounting tool, subsequent investigation found that tool remained partly unused despite showing its potential relevance for practice through user involvement. However, this does not necessarily signal legitimation-seeking behaviour. Reasons for not using some parts of the tool point to an overestimation of the functionality and an underestimation of implementation problems during the design process. The case also highlights the relationship between relevance and decision making.