The MPA cable is about 87cm long, so it should be able to stretch from you trouser pocket and allow the microphone to sit close enough to your mouth, for clear speech pickup. However, Shure's choice of clip is somewhat questionable. Because the clip is attached to the cable, rather than the microphone, the mic/button unit tends to hang at a downward angle, rather than pointing up, as you'd want it to. Personally I'd rather have seen the clip attached to the microphone, making for a tidier cabling arrangement.
It's also a shame that you can't control the volume from the MPA, although there is a limit to the amount of functionality available through the headphone socket. One answer would have been an impedance based in-line volume control, which Shure already bundles with its high-end earphones. I'm not a fan of this type of volume control, but ultimately you wouldn't have to use it if it was there, and there will always be those who'd welcome it.
Like pretty much everything that Shure makes, the MPA doesn't come cheap at around £40 - but also like pretty much everything Shure makes, you do get what you pay for. If you already have a set of Shure earphones that you'd like to use with your iPhone, then the MPA is, quite simply a no brainer. If you're using a different brand of high quality earphones, then the thought of having a mass of cable hanging around your torso may put you off. But then, if that does put you off, you're pretty much deciding that you're going to have to unplug your earphones every time your phone rings.
Shure has come up with the perfect solution for everyone who can't bear the thought of using Apple's bundled headset with their iPhone. If you've already got a set of Shure earphones this is a truly killer product, and if you haven't go get a set of SE210s and an MPA to go with it.
The downsides to the MPA are the poor clip implementation and the fact that it's pretty expensive, especially when Gordon has already dug up news on a similar product that is set to cost a fraction of the price. That said, I have no idea how good the sound quality will be from that device, whereas the MPA excels. Needless to say, I'll be carrying my Shure MPA with me everywhere I go from now on!