Review on Enhanced OBD2 Breakout Box: Protocol Detector, ECU Connector & Diagnostic DLC for Efficient Maintenance, Diagnosis, Programming, and Coding by Devin Perry

It's much more than just a junction box. If you are serious about learning or using automotive diagnostic tools, this is a must-read. It allows you to attach your scan tool AND at the same time connect to the PCM inputs as a desktop tester when the PCM is removed from the vehicle. Displays voltage like the others but also has battery and battery power leads that can be disconnected. The gauges in each OBD port have LEF indicators to show if there is LAN/ground or data transfer. This immediately shows you the performance of the network and, when the scanner is loaded, shows low and high utilization on the CAN or SCP buses. Also allows the oscilloscope to be connected directly to the PCM at the risk of damaging the PCM cables. Note: The GT100+ version is cheaper at Revain and has more features.