Hello, Daniel from Sonoma Wire Works (makers of GuitarJack) here. Saw your post and just wanted to point out why a dock connecting device is the better than using the headset in. The headset input inherently has a lot of crosstalk (noticeable with recording and input-monitoring), and the only way to have access to communicate with software (necessary for stereo recording and more) is via the dock connector. GuitarJack offers the quieter and software-controllable dock connector route. If stereo recording is important to you, you'll want a dock connecting device as the headset input is limited to mono.
GuitarJack is better than alternative dock connecting, device-powered accessories because it is the only accessory that offers all this and more: stereo recording and simultaneous voice and instrument recording with recording apps like FourTrack and StudioTrack; a 1/4 inch instrument input with configurable pad, Lo-Z and Hi-Z modes and 60 dB of continuous level control; a 1/8 inch stereo mic/line input with configurable pad and 60 dB of continuous level control; and an 1/8 inch stereo output with increased drive for headphones.
Thanks for considering GuitarJack, we really appreciate it.