SiriusXM lifetime subscription for F150 question

I'd like to purchase a lifetime subscription radio unit off of eBay for the purpose of installing it in my 2004 Ford F150. I am aware that attempting to transfer service to another radio unit is not possible, and I'm willing to take the risk knowing that if the unit itself dies, there goes any chance of keeping the service. However, looking on eBay, I'm overwhelmed by the options. What is the 'holy grail' that I should be looking for, the one everyone wants but are hardest to find? I know how to remove the front dash panel in my vehicle, but aside from that I'm pretty unknowledgeable regarding SiriusXM units as well as vehicle audio. My vehicle does not have built in aux input, so if there's a model-specific that would add that functionality it would be nice to have, albeit not completely necessary, as I have a bluetooth FM transmitter that plugs into the 12v outlet. I see on eBay that some units are advertised as having Howard Stern vs not having Howard Stern, what do I need to be on the lookout for so that I don't end up purchasing a unit that is missing content I might have otherwise potentially been interested in?

This is a bad idea. Anyone who sells you a unit with a lifetime sub on it can easily transfer that sub or disable it after they sell it to you. They could do it in a day, week, month, or year from now. They still have control over the subscription.

The only way I would ever recommend this is if you purchased it from someone you knew and trusted, like a family member or best of friends.