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[Display omitted] • Significant progress in both research and industrial development of PFR systems. • Improvements include innovative design, optimized operation and enhanced mixing. • Technical/economic MCDA of mixed PFR with and without internal moving parts. • Mixing without internal parts has better efficiency and simpler operational needs. Plug Flow Reactors (PFRs) are widely recognized for their cost-effectiveness due to lower initial investments and start-up expenses in comparison to alternative systems. However, PFR face substantial challenges, including inadequate mixing leading to low mass transfer, potential issues related to thermal stratification, and complications arising from solid sedimentation. Furthermore, concerns related to floating, or scum formation highlight their limitations in diverse industrial applications. Recent years have witnessed significant progress in both research and industrial development pertaining to PFRs. This progress primarily focuses on improving PFR performance through innovative reactor design, optimized operating conditions and enhanced mixing. This review provides an extensive overview of these advancements, as identified through bibliometric analysis and literature review. The review delves into various retrofitting approaches for PFRs, exploring their impact on digester stability and methane production. Finally, the authors adopted a multi-criteria decision analysis (MCDA) to compare, from a practical/industrial perspective, mixed PFR systems with internal moving parts to those without. The evaluation relies on two criteria categories: technical and economic. The results revealed that mixing without internal moving parts excels in energy efficiency, reduced maintenance, lower contamination risks, and simpler design. Recommendations for future work are provided accordingly. [ABSTRACT FROM AUTHOR]