I've only used it via Wifi and since we are in roll out mode for 3G, it seems that it is up and down, so I am mostly on Edge right now. I've not even bothered with it.
I can tell you that the XM side uses music dock, which doesn't or hasn't updated their channel listing so that is rather confusing, though they did add the channels directly to Pocket Tunes in a recent update, which makes it a lot easier. The pad data is hit and miss, though I've learned how to make it work.
It will do the job, but personally I am finding I am not using it much now and have gone with the Sirius XM app instead. I am not totally happy with it either, but it is a bit more refinded for Sat radio vs and Pocket Tunes which covered tons of music stations etc.