A magnet on the rear of the device attaches to an included clip, making it really easy to attach the Crystal to a car visor or any other convenient place. Or in my case, even the fridge! The clip conveniently doubles as a mount for the Crystal, too, when placed on a surface or counter. It's a simple design, but it works effectively.
Pairing up the Crystal to my iPhone was as easy as any other Bluetooth pairing. Once paired for the first time, the Crystal will automatically pair itself back to your phone with a notification beep (with Bluetooth turned on) whenever it's in range (up to 10 meters). And if you happen to have two cell phones, the Crystal can be paired to both at the same time.
Using the Crystal to take and make calls couldn't be easier, especially with an iPhone 4S using Siri. Pressing the multi-function button (think Home button) on the Crystal activates Siri, so you can make a call or send a text totally hands free as well as all the other benefits Siri has to offer.
Similarly, if your phone rings, simply press the multi-function button to answer or end the call. I didn't have a previous generation iPhone to hand, but I suspect using the multi-function button when there are no incoming calls would activate voice dialing. Of course, you can always take, dial or end a call by using your phone the normal way and simply use the Crystal as a speakerphone.
There are four other buttons on the Crystal, two on each side: volume up, volume down, power on / off and end. I couldn't figure out what the "end" button did (it didn't end calls). Using the multi-function button seemed to achieve all phone functions I required, including ending a call. When the Crystal is activated, all the buttons light up, making it easy to operate in the dark.
Sound on the Crystal was anything but crystal clear, but it was absolutely usable, if not slightly muffled. The Crystal can get loud, although at full volume audio became distorted.
For the most part, the built-in mic seemed to pickup what I was saying with no difficulty for those on the other end, so long as I was facing the device when I was speaking. Siri had no more difficulty understanding what I was saying than in any other scenario.
The Crystal has a built-in, lithium ion battery, providing 20 hours of talk time and 40 days of stand-by. The battery can be charged in 3 hours with a micro-USB cable.
Bar a few minor niggles with audio quality and the particularly cheap feel of the device, the SuperTooth Crystal works really well -- whether you're using it for hands-free driving or simply as a speakerphone. As an iPhone 4S user, there's an added bonus with the Crystal simply augmenting Siri's functionality.