Connecting the MM200s to a Bluetooth enabled player couldn't be simpler. I used an HTC Touch HD that I happened to have sitting around, but an MP3 player like the Samsung YP-P2 would do just as well. Press and hold the play/pause button until the status LED flashed red and blue alternately, search for the MM200 on the device, type in the ever-secure 0000 passcode and, on a phone, decide if you want to use the device as a hands free adapter, stereo headset or both.
Thanks to the A2DP Bluetooth profile, audio quality isn't compromised heavily by the connection (capable of 731Kbps max for the interested), unless you have an iPhone or iPod touch which both bizarrely don't support A2DP - so bear that in mind if you own such a device. In-call audio is as good as could be hoped for, wandering around the TR office grounds (there are some advantages to working in the middle of nowhere) I was able to talk to and hear Riyad perfectly so there's no complaints on that front.
Moving to a bit of music, I was pleasantly surprised by the MM200's audio quality. At £75 I hadn't expected much, given Sennheiser is charging for the Bluetooth module and a pair of earphones, so I was pleased those preconceptions were wrong. Firing up a 320Kbps MP3 of Placebo's Running Up That Hill (a cover of the Kate Bush original), I was pleasantly surprised by the clarity and bass produced. The ety8s definitely produced a fuller, warmer sound, but at twice the price I would expect no less.
A quick listen to the wonderful The Darkness track Girlfriend proved an enjoyable experience, with even the highest of Justin Hawkins' high pitched shrieks (which are a good thing, I assure you) fully reproduced, as were the cracking guitar solos.
The only major criticism with the MM200s is the slightly narrow soundstage produced. Whether that's a fault with the earphones themselves, or the Bluetooth connection I couldn't say and it's not that noticeable anyway.
Plugging in a pair of similarly-priced SE102 earphones, I can definitely say that Sennheiser has sacrificed the quality of the earphones used on the MM200s in order to compensate for the added cost of Bluetooth. If you need, or want, the wireless connectivity, though, that sacrifice is one you'll just have to make.
If you're after a set of Bluetooth earphones then the Sennheiser MM200s are definitely worth considering. A great form factor, commendable audio performance and, of course, the convenience that wireless connectivity offers all wrapped up with a decent price.