It fits well into my Cooper, and does a great job of holding my iPod Touch so I can change tracks without crashing.
The only problem is that it is not designed well for the Touch, as the headphone jack is on the bottom of the unit, unlike the iPhone. This is now concealed by one of the supporting legs on the cradle and cannot be accessed. It will be fine for iPod compliant stereos that use an iPod cable, but not for AUX-type 3.5mm cables.
It can be gotten around by fitting the iPod upside down in the cradle as it can be rotated through 360 degrees, you will just need to make sure it is held securely and does not drop out when going over speed humps etc. My iPod has a rubber case so is pretty well gripped when fitted, but I may end up taking a Dremel to one of the legs in the future to let me access the jack.
All in all I recommend the mCup, but bear in mind it may not be perfect in all cases.