Conclusion: Smallest of the Sirius car-mount portable radios (but not that small), Sportster Replay buffers 44 minutes of the channel you're listening to. Check out the bufferless Sportster for $80 less.
Pros: 44 minute music or talk buffer. Good sports programming.
Cons: Buffer flushed when you change channels or power down. Bulky compared to XM's smallest. None (it's pretty easy).