Multi-agent systems (MAS) are increasingly being exploited to support autonomous recommendation of products and information to contemporary application users. Multi-agent system product lines (MAS-PL) promote large-scale reuse of common and variable agency features across multiple MAS applications. The development of MAS-PLs can be achieved through alternative MAS-specific frameworks (JADE and Jadex), and general-purpose implementation techniques, such as aspect-oriented programming (AOP). However, there is not much evidence on how these techniques provide better modularity, allowing the conception of stable MAS-PL designs. This paper reports an empirical study that assesses the modularity of a MAS-PL through a systematic analysis of its releases. The study consists of a comparison among three distinct versions of this MAS-PL, each one implemented with a different technique: (i) Jadex platform and configuration files; (ii) JADE platform and configuration files; and (iii) JADE platform...