Yeah, what it essentially does is con the headunit into thinking there's a changer attached (so opens up the line input channels) but without any controls like disc/track skip
You can achieve a similar result + have the option of a changer, if you use an aftermarket changer (Sony, Panasonic etc) and an adapter box ... the red and white phono leads from the aftermarket changer lead usually plug into the box which feeds into the headunit -
if you unplug these and plug your iPod into the adapter, the CDs will load and play in the changer as before but you'll get the sound from the iPod ... kinda like a cheap AUX in
If you want to be really clever, you can use a phono switch in the glovebox from somewhere like Maplins to toggle between iPod input and normal CD changer input.
(has to be an aftermarket changer though, cos otherwise you've got to start splicing into looms and it gets messy)