IF you have a stock radio you may need to pull the head unit anyway (IIRC the antenna has a screw holding it in and if not it may at least be very stubborn)
As for the adapter..yes it works very well. I have an Onyx and used one for it. Fair warning..you will need two antenna adapter cables to hook it up though. One plugs into the head unit and connects to that adapter...the other connects from the adapter to the antenna cable. I picked the cables up from Best Buy for about $15 a piece I think. They should have them in stock but you will have to ask for them.
Incidentally, I got my adapter with a power hook up as well (came with the kit from Crutchfield). I pulled the head unit, and spliced it into the radio power lines so that the XM comes on with the radio.
Ultimately I ran the cables into the center dash vent and between the plastic, down behind the radio and then tucked the whole thing in behind the radio. I have the XM on the vent mount(for now) and you only see about 2 inches of cable this way.