The digitisation of transport services has led to the implementation of so-called demand-responsive transport (DRT) systems with varying setups and goals around the globe. Numerous approaches have been made to account for differences in the local circumstances and regulations to achieve the most successful outcome for those services in both, rural and urban areas. The reasons for their widespread popularity are the envisaged benefits of economically reasonable operations combined with ecologically and socially beneficial traffic. Yet, while some DRT systems persist over an extended period, many fail to become a permanent passenger transportation option, especially in rural areas. This paper shall explore parameters suited to measure the success of a DRT system and structure their inter-dependencies. Firstly, the paper presents types of flexibility and their different gradations in order to classify varying systems. Secondly, suitable and already used parameters to measure figures of DRT systems like travelled distances and vehicle occupations are examined and with their respective application cases lucidly compared. Thirdly, the paper proposes a four-step evaluation framework and discusses existing and new approaches to comparing the success of different flexible transport systems and future possibilities.