Typical feedback ammeters cannot measure above 20-30mA because the current actually flows through the op-amp and most op-amps can't handle much current. This one has it's output buffered by a PNP transistor (I would make it a FET if EveryCircuit's FETs weren't so weird), allowing it to handle much higher currents. It does still have limitations, the op-amp's output hits the power supply rail at a few hundred mA.
