Background/Objectives: This study aimed to compare the final impressions obtained using three different impression techniques in completely edentulous patients, focusing on the clinical applicability of the JB Tray^® for immediate custom tray fabrication with a polycaprolactone-based thermoplastic resin. Methods: Five edentulous patients were recruited for a preliminary clinical evaluation, and three impression techniques were tested: (1) JB Tray^® (JB), which allows simultaneous border molding and final impression taking; (2) the conventional modeling compound border-molded technique (MC, control); and (3) the one-step silicone border-molded technique (OS). All impressions were made by a single prosthodontist, and the internal surfaces were digitized using a 3D scanner for analysis of internal fit. Each arch was divided into reference regions for quantitative comparison. Statistical significance was set at p < 0.05. Results: Color map analysis (threshold of ±1.0 mm) revealed that the JB Tray^® group exhibited wider border extension in both the maxilla and mandible compared with the modeling compound and silicone groups, with a more pronounced effect in the mandible. However, no statistically significant differences in overall internal fit were observed among the three methods (p > 0.05). Conclusions: These preliminary results due to small sample size suggest that the JB Tray^® enables efficient impression taking in edentulous patients and can serve as a viable alternative to conventional custom tray techniques. Further research with a larger sample size is warranted to support widespread clinical application.