This mic is an excellent option for recording vocals on the go. I use it to record tracks (mainly rap) with my iPhone. Although the labeling of the buttons is not very clear, it is easy to figure out what the functions of this microphone are.
The upper button adds wet signal to your monitoring from your recording app of choice in incremental steps. Although it might be a little limiting, I find this solution usable. The bigger rotating knob adds gain. Pressing the big rotator knob mutes the microphone.
The feature that shaves off one star is the small size of the diaphgram. This might be useful, if you record in a space with lots of room reverb. Being mobile it is easy to find a spot where room reverb is not an issue. The small diaphgram prevents you from getting that huge studio sound out of the microphone. Nevertheless, the sound is better than one would expect from a mic of this size. Also, the A/D is pretty much flawless, giving you pristine audio quality. I have never experienced any glitching or crackling with this microphone. It is what one can expect from an Apogee product.