It is worth understanding what impedance means with respect to fuel injectors.
A fuel injector is just a solenoid. When you put a charge across the winding, a plunger is pulled back and a path is opened for pressurised fuel to pass through to the pintle.
The voltage required to activate the solenoid depends on the size and winding of the solenoid.
The winding has an electrical resistance (impedance), and the voltage used to activate the solenoid has to be matched to the solenoids electrical resistance.
The GTIR injectors are low-impedance which means the electrical resistance of the solenoid is low.
The resistor pack (bolted to a bracket next to the wiper motor) takes the 14v in from the cars power system, and reduces it to 5v and passes 5v to each of the injectors.
The ECU switches ground to each of the injectors to activate them.
An injector that has low impedance cannot be driven by 12v. Ours are driven by 5V.
High impedance injectors (with high electrical resistance) can be driven directly off the 12-14v of the cars system.
A manufacturers decision to use low or high impedance injectors used to be determined by the power of the ECU driving them.
If you drive low-impedance injectors with 14v, you're putting a lot of heat back into the transistors on the ECU that are switching GND to the injector.
There isn't really a quality or performance difference between low/high impedance.
peter