We have thoroughly tested MicW and IMM6, and our conclusion is that they do not improve on the performance of the built-in Apple device microphones, whether the iPhone mic or the supplied headset mic, other than in appearance, and in the fact that it is a couple of inches away from the iPhone.

Basically you are trading one small-diameter electret condenser capsule for another, with similar performance.

This is because any mic that plugs into the headset connector is subject to analog processing. There is no way to avoid the effects of the severe Apple low-frequency roll-off filters and limiters, so any mic plugged into the headset connector suffers from the same problems.

Also, we have recently discovered that due to the design of the headset jack, if you turn on the output you will get bleed, sometimes severe, back into the mic input. 

Therefore, although it would be great to have a moderately priced microphone that performed well, we do not recommend spending money on this device, as it will not improve the performance of AudioTools.

iOS 6 update: We have been able to defeat the internal low-frequency rolloff filters in iOS 6, using AudioTools 4.7. However, even in iOS 6, we see no improvement in frequency response, or flatness, with micW or iMM6, over the Apple-supplied internal  mic.