It was between this and the Belkin one. Reading the Belkin reviews about range, I opted for this one even though it cost $6 more at the time. First impression was that it is so easy to setup, at least with the iPhone 4, but I can't imagine it being more difficult with other Bluetooth A2DP audio players. You don't need to enter any codes, just press the connect button on the device (LED will start flashing green), go into the Bluetooth menu on the iPhone and select the Logitech adapter. After it connects the LED becomes solid green, that's it! However, the iPhone will not automatically connect to it next time, you have to go to the Bluetooth menu on the iPhone and connect to it again manually. That's probably a good thing in my case because my wife connects with her iPhone too sometimes so we don't want it to automatically connect to mine or hers. This might be a little cumbersome to some, but at least you don't have to go through the initial connection process again, i.e. pressing the connect button, the 2nd time you connect, even if you have paired multiple devices to it, like both my and my wife's iPhone... not sure if there is a limit on how many you can pair at once though. The only hassle I found is disconnecting, you either have to turn off the Logitech adapter (i.e. unplug it) or turn off the Bluetooth radio on the iPhone (or go out of range I suppose). Perhaps I missed something about how to disconnect, please let me know if I did! Also, if nothing is connected to the adapter, the led will be red.
The range is very good, good enough for my needs. I can get about 25 feet away from the device before it even hints at dropping the signal, and that include one wall between the adapter and my iPhone AND if I stand directly between the two. I'd imagine line of sight without obstructions could get at least 30-40ft, but I'm sure it would also depend on the Bluetooth radio in the audio player you use.
Sound quality is darn good, this was my biggest worry because I am connecting it to an Onkyo receiver, albeit a slightly older model TX-SR502. I can't say I have the best speakers (Polk RM6005 and PSW10), but they are good enough to tell the difference between, for example, a 128kbps encoded MP3 and a 192kbps one. Furthermore, all the MP3s I play from my iPhone are at most 192kbps so it's not like I have the cleanest source material to begin with. That being said though, I have no complaints at all about the audio quality. For all intents and purposes, I cannot tell the difference between the Bluetooth A2DP and a direct wired connection out of the dock port. A cool thing I have on my receiver (and probably a lot of other ones too) is that there is a switched A/C outlet on the back of it that turns on and off with the receiver power. I just plug the A/C adapter of the Logitech into this outlet so it automatically turns on and off with my receiver, it's as if I had a built in Bluetooth radio on my receiver :)
A few things about interfacing with the iPhone 4.
1) When connected to the iPhone 4, you can still control the volume via the iPhone. This is something I didn't expect because when I think line-out, I see this device as a wireless line-out, I only expect to be able to control the volume via the receiver it is connected to. I suspect this added volume control might degrade the sound quality a little bit. Regardless I can see how it might come in handy even if I will almost never use it. Good thing is, by default the Bluetooth A2DP volume control is at max, which makes it a decently loud input signal to your receiver.
2) When the Logitech Adapter is powered off when still connected to the iPhone 4, the iPhone is smart enough to stop playing music automatically, kind of like unplugging headphones while playing music.
3) Sound effects from games and YouTube videos, etc... are directed over the A2DP wireless signal too. (PvZ on surround speakers anyone?!)
Overall, I'm very satisfied with the product, but I don't think it's worth $40 though, maybe $30 tops, it's such a simple device. But I was in a hurry to get one so I didn't wait.