Well, it didn't really work. First, there was a noticeable amount of noise when the music was quiet; fiddling with the volume controls on both the player and the radio did not help. The noise got a little more noticeable when the transmitter was used with batteries (as opposed to the included DC power adaptor). Even worse/better, if I used the windshield wipers, there was horrible interference. Cripes, what is this, AM RADIO ?
I should have known better when the nice lady behind the counter suggested that I try an alternate brand (iBeam ? I'm trying to suppress the memory now), but the results might have been only marginally better, and just not acceptable.
So now I'm back to the “primitive” cassette adaptor solution, which of course is awkward and old fashioned, but it works. It's definitely more distorting than a simple piece of wire, but at least it's not noisy and at the mercy of the ether.
Really, it would be nice if more car stereos just had a line input on the front – and some do, like the cheap Aiwa deck that I'd bought for the Neon five years ago. Until direct connections like that become more common, we'll have to suffer the indignity of these imperfect solutions.