Carbon capture and utilisation are crucial for reducing fossil fuel dependence and transforming the chemical and energy industries. Microbial electrosynthesis (MES) is a promising technology where electrotrophic microorganisms convert CO₂ into valuable biochemicals using electricity. Despite recent advancements, replicability in MES remains poorly understood, with scarce pre-inoculation abiotic data and limited exploration of abiotic and biotic performance correlations. This study introduces a novel miniaturised reactor, modelled after a state-of-the-art flat-plate directed-flow-through bioelectrochemical reactor (DFBR). Four miniaturised reactors were tested in parallel under abiotic conditions to evaluate the impact of electrode material, reactor design, and assembly on replicability of electrochemical behaviour. Using the dynamic time warping (DTW) algorithm, reactor similarity was quantified for the first time based on electrochemical performance. Kernel scatterplot smoothing on micro-CT data revealed that electrodes, particularly the commonly used carbon felt, are a significant source of variability in electrochemical performance, as further supported by additional abiotic electrochemical tests. Additionally, the miniaturised reactors were inoculated with an enriched mixed culture to examine microbial activity's effect on replicability, achieving concentrations up to 4.55 g L^-1 acetate, 0.96 g L^-1 butyrate, and 0.38 g L^-1 caproate after 60 days. Variations in abiotic conditions, including maximum reachable current density, onset potential, and porosity, influence biofilm growth and performance. The miniaturised DFBR effectively represents the serpentine DFBR, while the adaptable reactor design and proposed statistical methods set a new benchmark for MES research.