The OEM unit is more expensive and has fewer features. the DICE module should allow you to control via your iphone. I bought a USA spec module having not known of the DICE yet, and it basically emulates the BMW unit.
a few other points. since the ipod classic came out, all new model ipods(including iphone) with new software version don't work quite the same. example, i can't get text on the display when i have it set to ipod control. i can get text when im on hU control, but the ipod controls are then locked. the hybrid mode that allows you to control both wont work on the new ipods. i'm not 100% but i believe the DICE unit has the same issues. i bought an older ipod video off a friend and use that so i can use the ipods controls and still get text and use the HU controls.
if you personally install any unit you should be able to put the ipod wherever you want, your not limited to the glove box, i have mine in the sunglass tray, its a great spot for it, very accessible. installation was very easy. there are many helpful DIY on this forum.
another point, controlling using the iphone while driving is tricky and dangerous. i don't like it at all. i know it may not seem much different, but i have much easier time controlling my normal ipod while driving than my iphone, the difference is significant.
lastly, im not sure if the new cables are out yet, but the iphone wont charge with any unit i know of. this is important because every time you plug it in or change a song with the steering wheel controls or deck controls, the iphone lights up with a message saying "this accessory was not made to work with iphone. do you want to turn on airplane mode?" its extremely annoying. it comes up ALL THE TIME.