The second piece of the X2's puzzle is an FM transmitter that outputs audio on the FM radio band, which can then be received by any FM radio that is within a short range and tuned to the proper station. Unlike most FM transmitters and radios that we've seen, the X2 can be set to transmit on both even- and odd-numbered stations, which potentially gives access to more open frequencies. These frequencies can be manually selected by rotating the control knob or an autotune feature can be used to automatically search for the cleanest open channel for audio transmission.
The combination of an FM transmitter, Bluetooth connection, and analog audio connections gives you three ways to use the X2 as a bridge between your handset and car stereo: Bluetooth-to-FM transmission, auxiliary-input-to-FM transmission, and Bluetooth-to-auxiliary output. We suppose that one could use the auxiliary input with the auxiliary output, but that just seems unnecessary.
Although we tested the Gogroove FlexSmart X2 in all three of its connection modes, the bulk of our testing was performed using it the way we think most consumers will: as a Bluetooth-to-FM bridge.
Pairing mode is initiated by pressing and holding the call button for 2 seconds. As mentioned above, our test Android phone was able to pair with the X2 automatically, skipping the four-digit PIN entry process. Once it was paired, we tuned the X2 to an FM frequency known to be empty, tuned our car's stereo to the same frequency, and hit play on our handset's MP3 application. As expected, music then played on our car's stereo. Of course, audio quality is limited to the lowest level in the chain, so in this configuration that meant the relatively low quality of the FM radio broadcast. Audiophiles will be severely disappointed, but for many people (including heavy podcast listeners) the ease of installation may be well worth the minor degradation in audio fidelity.
That said, the audio quality of the X2 we observed during bench testing was on par with some of the best FM transmitters we've tested. Your mileage may vary depending on how crowded the airwaves are in your area. In vehicle testing around hilly San Francisco, we found that a frequency that worked in one area of town was completely unlistenable in another, leading to a good deal of frequency changing as we ran our daily errands. This is an inherent weakness in all FM transmission technology and not a flaw in the FlexSmart X2's design.
To increase audio quality, we used the Bluetooth connection to output audio through the line output into our car stereo's auxiliary input. However, if your vehicle already has an aux-in, a $5 audio patch cable would yield even better quality than this $50 transmitter. If you're not looking to use the FM connection, this isn't the car audio option for you.
If you're no audiophile and you're simply looking for the easiest way to hear calls and music from your high-tech phone through the low-tech FM radio in your car, perhaps the Gogroove FlexSmart X2 is the stereo adapter for you. Its use of both Bluetooth and FM transmission wireless technology means that in most cases you can simply hop in your car, hit play, and go, without fumbling with wires or cradles. However, it includes connections and cables for the times that you do want to, for example, plug in and charge your phone.
There are a few weaknesses in the X2's design. The basic display gives no caller ID information, meaning that the phone's screen will need to be visible to discern incoming callers. Likewise, the lack of voice dialing means that you'll still need to use the handset when initiating a call other than a basic redial.
For a few bucks more, we'd recommend that prospective FlexSmart X2 purchasers also take a look at the Motorola Roadster, a visor-mounted device that offers the same capability of bridging FM and Bluetooth calls and audio, but also includes an internal loudspeaker and rechargeable battery for use outside the car, a superior noise-cancelling microphone with basic voice command, and integration with the Motorola MotoSpeak app for Android and BlackBerry.