How about getting both? A CD changer and
this? Not much for the unit, can be used in multiple vehicles, or even inside w/ an external antenna. You would still have subscription, however w/o much invested in the XM unit you could cancel after a few months if you didn't like it.
Disclaimer - I don't know much about this unit. You may have to pick up a vehicle kit, I'm not sure. Check around.
www.xmradio.com