The Scosche FM-MOD01 is still an FM modulator and transmitter, the only difference is that it injects a lower power transmission directly into your antenna input.

When powered on, the FM-MOD01 "breaks" the connection with your regular radio antenna and feeds the modulated signal to it instead.

So the result is no interference from FM stations which might interfere as with the normal "over-the-air" FM modulator/transmitters.

The give back is that you'll have to turn it off in order to use your radio normally.

The other thing to consider is because it still uses FM and the FM tuner in the head unit, you're still not getting the full frequency range (20Hz-20kHz and pretty darn good flat response at that too) that your iPod might be putting out (depends on your source quality of course).

FM's carrier signal is located at 19kHz so most FM Stereo radios roll off their frequencies starting at about 15kHz and most radios will go down to about 50Hz.

That said, I've never brought my spectrum analyzer into my Crossfire so I'm not sure what the system and speaker's response is like in the cabin so it may or may not matter.