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BIG NOTE: *** New Addendum*** Apple has finally fixed the bluetooth compatability problem in the most current version of MacOs (OSX "Mountain Lion").
For the first time, I have had the MW-600 achieve a connection to my iMac and maintain it, in constant or in intermittent use, until the battery on the MW600 runs down. You can now use the MW600 to walk away from your Apple Computer to do the dishes during commercials or get a soft drink and nothing bad will happen.
More cause for celebration: the MW600 just bought itself an extra star!
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*This is the full, original review. New notes are in parentheses*
The Sony Ericsson MW600s are not perfect, certainly not a panacea, but they function well in multiple roles; offering a stereo bluetooth headset that allows the option of using high-end headphones for improved sound quality and isolation. I voted for them with my own money and, so far, I would be more than happy to buy them again. (I finally destroyed on set after more than year's use--please never ask me how--I bought a new one, in white this time, and I am thinking of buying a second one for dedicated use with my computer for audio and Skype-calls).
Before going on to talk about the real, solid reasons for liking them, it is necessary to get other people's reasons for disliking them out of the way. The MW600 has characteristics that some who have reviewed it have called problems. The following things are true about the MW600:
1. It is not made of solid titanium.
2. It doesn't fit a keyboard's worth of controls onto a two-inch cylinder.
3. It offers only partial compatibility with Apple products. (fixed! 08/17/12)
4. It is not so simple to set up that a monkey in boxing gloves could do it blindfolded.
Now, the good stuff.
Physically, the MW600 bluetooth stereo headset is a short, black cylinder with its sides forming a triangle. A clip with a light spring is attached to one angle of it, while the other two angles house controls that let you attach it to devices and control it using a black-and-white, organic light-emitting-diode (OLED) display.
Its overall length without headphones is shorter than my pinky and yet it interfaces with many bluetooth-equipped computers, smartphones, and music/movie players with limited compatibility with Apple's iPod Touch and iPad (this has since been improved in later versions of iOS and OSX Mountain Lion. 08/17/12)
Unlike it's predecessors, the MW600 has a headphone jack instead of fixed headphones meaning that it can accept any stereo headphones with a standard 3.5mm plug. The headphones that come with it have a short cord and offer very good reproduction for the sort of sound that comes from a portable player, but the fact that you can plug anything you like into them offers you the option of swapping out the units that come with it for better headphones, including audiophile-level units (high-impedence units like Grado SR-60s will work with the MW600, but it doesn't have the oomph to get the best from them, nearly all buds are okay and some are surprising. 08/17/12).
For people who need better sound or louder volume this is a definite cause for celebration. It means convenience: it means that users with high-quality, two-part headphones of the kind made by companies like Shure and Denon can integrate them into their telephones via bluetooth for enhanced call-quality; it means that exercise-lovers can use high-end equipment while running on treadmills and it means that someone sitting in a cafe can stand up and stretch without having to disassemble their set-up first.
Call quality on the user's end with the MW600 is as good as you can expect when the sound of the caller's voice is sent directly to both the receiver's ears while MW600's microphone seems adequately sensitive and wind-resistant.
Of course, nothing is perfect and the MW600 is no exception. The MW600 is not for people who can't be bothered to learn control sequences of simian complexity, or who are too sensitive to put up with the limitations of an interface that runs off of four buttons and a (slightly frustrating) volume slider to control a device that is smaller than the average matchbox.
Also, Sony and Apple are not the best of friends and the Sony device's music controls aren't recognized by Apple devices, including computers (this has changed, the MW600 will now connect reliably to an iMac running OSX Mountain Lion 08/17/12). The MW600 will interface with and play output from Apple devices, but the controls on the MW600 only play/pause the iPod Touch/iPad. They will not fast-forward, select, skip or do anything else to the actual music sequence.
This means the user of any of Apple's i-devices will have to undergo the ultimate hardship to change tracks or playlists: he will have to reach into his pocket and use the iPod's physical controls, supporting the brutishly heavy machine in his hand for second, after grueling second...
At the end of the day, it is hard to call the MW600 a bluetooth device because it goes above and beyond the great majority of bluetooth devices, offering a power and flexibility that makes it better than nearly everything out there, including stereo units like the Motorola Motorokr M9s and single-ear bluetooth units like the various Jawbone devices that can cost nearly twice as much. Even paired with good headphones, their sound is never as good as a metal-to-metal connection's is, but with good headphones, for bluetooth, they're a revelation.
Oh, I almost forgot: they threw in an FM radio for free.
(addendum 08/15/2010: After several hours of listening to an audiobook on my iPod Touch at work, the iPod touch ran out of power (in part because of the high power demands of using bluetooth). I set it on a charger a substantial distance from where I was standing and I found that I could still keep listening to it using the MW600 with no loss of sound quality. The pause/play function worked fine with me standing where I was with a closed door between myself and my player.)
(addendum 09/01/2010: Trying to use this device, sharing it between multiple Apple devices, can cause frustrating connection problems. After connecting it to my computer, iPod Touch and iPad, I soon found it necessary to erase profiles and start over from scratch when connecting. Other companies make bluetooth gear that handles this more easily. Also, the general incompatibility of Sony and Apple bluetooth hardware (mentioned above) can cause problems on the computer side when you attempt multiple pairings with devices of the same type (largely fixed, as of 08/17/12).
I still like the things (I've used them to listen to an audiobook playing on an ipod that was charging 30 feet away), but I have to say that I like them less (they're much improved in value by the enhanced Apple-compatability 08/17/12)