I use my Legal SIN to get a place to live, to drive around, make purchases of basic stuff.
But yeah, your not wanting your firearms registered to that legal SIN so CSI can trace them to you.
You'll also want to be doubly careful about leaving evidence behind, photographic or DNA etc etc that can be traced to your Legal SIN.
Not that you should want to do that for a FAKE one either if your SINless, but at least that is only a new FAKE.
As for the OP, yeah, I think its considered Free, the cost of the FAKE is where the cost is, getting a Drivers, Firearms, etc etc license is pretty much covered by "Living Expenses".
Though I might put a limit of "Low or Better" on it so Street/Squatters can't have them free just to encourage not being cheap & living "Street" lifestyle.