I've had an XM Pioneer Inno radio for a year now. I like it very much.
What exactly do you need to know? For me to renew my subscription, it costs $142.45 for the year. Not cheap, so I justify the cost by listening as often as I can.
It's true, XM and Sirius finally merged. Their services were very similar, but I noticed programming differences between the two. (We have Dish Network, which came with Sirius.) For instance, I thought the 80s hits station on Sirius had a better variety of music than the 80s channel on XM. I thought the Big Band Sirius channel played more "big band" variety than the '40s channel on XM, which mixes swing numbers with more slower groups like the Mills Brothers and vocalists like <shudders> Vaughn Monroe.
Sirius had an 80s rap station which I loved. XM had "Rhyme" which was 80s and 90s rap, and I only liked it. Now the combined service has the Eminem channel which is 80s 90s and 00s rap. I don't listen to it very much at all any more.
Overall, though, my Inno gives me great portability. It's about the size of a cell phone and I can use it practically anywhere.
If you're sick of local homogenized radio like I am, satellite radio is a great choice. Note, I very much like the localness of local radio. I just don't like the programming. I like local morning radio shows. I like listening to local air talent. I don't like Howard Stern or other national talk shows.
But for music and other specialty radio like old time radio and comedy, satellite radio is awesome.