I tried an XM antenna once and it didn't work. It was also a little bigger and it bent the prongs inside the connector so I had a loose fitting antenna until I finally bought a new base for it. I wonder what was different about the one I tried vs the ones that have been working for some of you. Oh well, buyer beware.
I don't know what this guy did wrong, but that is totally not my experience. I use a car antennas every day at work. I replace them very frequently because the wire gets closed in the equipment doors, and get cut. I started buying XM antennas, mostly the micro2, because they are cheaper. They use the exact same SMB connectors so there is no danger in damaging your equipment. XM antennas work just as well, are more reliable, and cost less. Which is odd because xm car kits are way more expensive than Sirius'.