Bummer about RadioShark's mediocre reception; I live in an outlying area, where reception isn't THAT great to begin with, and in a basement to boot. I haven't given up on the fin though (yet).
I bought an arial from RadioShack, along with all the proper gear for grounding and shielding, etc., and mounted it on my roof. Even without a signal amplifier, my new FM feed is remarkable; I pick up many stations that I didn't think that I EVER would.
Despite this success, only my stereo receiver seems to register the signal, not the RadioShark. After giving up on the headphone/aux. out jack on the base of the fin (I tried soldering my lead to the ground vs. the left/right channels of a 1/8" audio plug, as Griffin tech support suggested), I pried open the top of my RadioShark fin, and straightened out its internal FM antenna so that it sticks straight out the top (even this minor alteration seemed to improve the fin's reception markedly). Then I hooked a 75 to 300 ohm transformer to my coaxial arial antenna feed, and ran the lead wire to the tip of my RadioShark's exposed antenna. Although the signal DOES improve, slightly, station reception, across the band, isn't nearly as good as from my Harmon/Kardon AVR 100 stereo receiver.
Shouldn't a clear FM signal, with the proper 300 ohm impedance, improve the RadioShark's reception as well as it improves my receiver's reception?