Mixing quality in polymer extrusion is critical when additives are incorporated through masterbatches. This work evaluates a patented rotational barrel segment (RBS) in a single-screw extruder, separately quantifying distributive and dispersive mixing and relating them to process trade-offs. RBS rotational speed and direction, barrel/die temperature, and a downstream Cut Rings section were investigated during dilution of a blue masterbatch in LDPE. From optical micrographs (50× and 100×, three locations), an image-analysis workflow provided a distributive index (DMI) and a dispersive index (DsMI), interpreted with the measured process variables. Counter-rotation improves distributive mixing and gives the highest mixing score (MixScore = 61.6 at Nb = −50 rpm vs. 57.9 neutral), at the cost of specific energy (3443.9 vs. 2590.9 kJ/kg). Strong co-rotation gives the best dispersive performance with the highest throughput and low specific energy (Nb = +50 rpm: DsMI = 52.7, Q = 6.54 kg/h, Etotal = 2482.6 kJ/kg). Raising temperature from 170 to 190 °C lowers pressure and energy but degrades distributive mixing. The Cut Rings section is beneficial only in an intermediate co-rotating case. The RBS therefore acts as an effective mixing variable.