The light on top goes solid blue when you get a successful pairing. Once connected, your smartphone or tablet can act as a remote, and you can stream music or other audio to the speaker while maintaining control of volume and track selection from the palm of your hand. In other words, you can sit on the sofa and choose to play any music file, app, or browser-based audio from these devices (including Pandora, SiriusXM, MOG, and iTunes) and have it wirelessly emanate from your stereo across the room -- no AirPlay or Wi-Fi necessary. The range is about 30 feet, but I managed to do a bit better than that.
As I said with the Logitech adapter, since Bluetooth is a wireless technology, you may occasionally encounter some hiccups, especially if you're walking around with the phone and stray out of range. Also, sometimes your own body (or somebody else's body) can be a source of interference and may result in a dropout. But my music mostly streamed fine over the course of a day's listening time in my office.
As for performance, Bluetooth compresses audio files, so you're not going to get sound that's quite as good as you'd get from Apple's AirPlay wireless streaming, which uses Wi-Fi technology and doesn't compress files. Bluetooth has a tendency to flatten things out a bit, so you might notice your music doesn't sound as dynamic as it should, especially if you're streaming to better speakers.
Add Bluetooth streaming to any speaker
Belkin vs. Logitech: So, which one is better?
The big question for a lot of people looking into this type of Bluetooth accessory is whether to get the Logitech or Belkin. That's hard to say because they do the same thing equally well. That said, I'm slightly more partial to the Belkin because it's smaller and cheaper. Though it lists for $49.99, it's widely available online for around half that price, which makes the street price a bit less than that of the Logitech.
I have no problem recommending either product to anyone looking for a relatively inexpensive way to turn a wired stereo into a wireless one. But if you can find it for $5 or even $10 less, the Belkin is the better deal.