Sirius FM antenna patch kit

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I saw in my local Radio Shack today a kit for Sirius satellite radios that allows one to run a line to the antenna jack of their car stereo directly while also allowing the car's antenna to remain connected. This would create a direct link between the Sirius receiver and the car stereo when the stereo is "tuned" to the FM channel selected for rebroadcast on the Sirius unit, but when tuned to any other channel, the car stereo would still receive regular radio signals. I'm having a good experience so far with using my FM re-transmitter, but this device holds some appeal for me because I don't enjoy fiddling with both my car's stereo and the Sirius receiver when I drive long distances and need to find different empty FM channels. Has anyone purchased one of these kits? I'm curious about how easy they are to install, if there's an improvement in sound quality, worse sound quality, etc.