Hello,
I have bought such a thing for my non-FIAT with a factory Blaupunkt radio, tested it OK, works fine (it was confirmed it is OK on the other make's forum) but uses the same plug as the CD-changer, so I had to choose. Next year I will probably install it in my girlfriend's car of same make. In my case it is plug&play. You only have to change the source on the radio.
As far as I remember the plug color defines with which cars it is compatible.