Pigtails are either OEM harness connectors (or just the OEM pin terminals with a length of wire crimped on) and are only going to simplify things if he is installing the OEM STI manual and thumb wheel switches. Even then I highly suggest installing it as-delivered since Jeff tests them before shipping. Once it is working fine then alter the switch configurations to your will.
The tap he is referring to is the TPS signal taken at the harness near the ECM connectors. 2006 WRX probably circuit B134 on pin B18 (RL colored wire), break out the DMM and check for signal change as you actuate the pedal. There are two wires with VERY similar insulation colors on that connector. If it looks good then remove some insulation, solder in, and wrap with e-tape.
Fusebox terminals might also help achieve an OEM-look for the power connection. You can use an existing and unused circuit, which will get you a factory fuse that is already there (hint fuse #18, 15amp, connector B271, pin B2) and supplied pwr at key ON and START.
vv I completely understand that