The Mikey Digital is much larger than the iRig Mic Cast, which plugs into the headphone port of your iOS device. The Blue device also features a swivel, so you can "aim" the microphone at your subject for the best possible sound. There are two other goodies in the box, a small carrying bag and a guitar jack adapter.
The Mikey D., as the user guide affectionately refers to it, has a sensitivity switch that toggles among loud, auto and quiet settings. Each setting has an LED associated with it so you get visual feedback of the switch setting. In addition, there's a 1/8" stereo input port (you use the adapter to plug a guitar or other instrument in for recording) and a micro-USB port in case you want to charge your device while recording.
No microphone is useful without an application to receive the input. When the Mikey D. is under the control of a recording / editing app such as GarageBand, all three LEDs light up. During recording, those LEDs will flash red if you're overloading the mic and clipping sound.
To test the Mikey D. under real-life conditions, I recorded the closing words from the Daily Update using both my regular setup -- a Blue Mic Yeti attached to my iMac -- and an iPhone 4S with the Mikey D. attached. In both cases, the app used for recording was GarageBand.
First, the Blue Mic Yeti on my iMac:
Now, the Blue Mic Mikey Digital on my iPhone:
Both sentences were recorded simultaneously, with the two microphones located as close to each other as possible. On the Mikey Digital, I set the sensitivity to "auto." The Blue Yeti is set in such a way as to be unidirectional, and the audio sounded somewhat more realistic and with less background noise from the fan in my iMac. The Mikey Digital picked up a bit more background noise, and the sound was less "warm" and "full" than what was captured with the Yeti.
It's important to note that neither of these recordings were post-processed. Removing background noise from both of the recordings would help, and the Mikey Digital recording could probably stand to have the low end boosted a bit.
The important thing to remember with the Mikey Digital is that it is meant for portable recording, and for that purpose I think it does the job better than any portable mic I've tried so far. For off the cuff recording, I'm probably not going to carry along a MacBook Air and my bulky Yeti. Pulling an iPhone out of one pocket and the Mikey Digital from another is the perfect way to have a very capable sound recording studio for music or voice anywhere.
Blue Mics really hit the ball out of the park with the Mikey Digital. Compared to earlier models of the Mikey and to other "made for iOS" microphones, the capabilities and sound quality of the Mikey Digital are significantly better.
Attractive and well-built, without the cheap plasticky look of competitors
Excellent stereo sound capture
Ability to plug a musical instrument into the microphone via the 3.5 mm stereo input port and the included guitar jack adapter
Clipping indicator helps during setup of microphone to make sure you're not overloading it
Adjustability of the Mikey Digital swivel provides a way to capture the best quality sound while still keeping an eye on the recording app
Dock connector might not work with future iPhones and iPads, or may need an adapter to work with them
Who is it for?
Professional and amateur musicians, reporters, podcasters, bloggers, or anyone who needs to accurately reproduce sound in stereo from an iPhone or iPad