You get the benefits without pledging. You need to buy in Torval Space, but you can sell anywhere (best price usually ALD or Dechaine).
I don't think is correct.
You get the Torval trade bonus if you are pledged and rank 2+ IIRC.
Because Torval opens up Imperial Slaves everywhere she controls, Supply goes through he roof (lots of Fed Citizens jump at the chance to be indentured servants rather than homeless I guess), and thus price drops to very cheap and stays there. So this is what is making it feel like a global bonus.
The trade bonus is on profits, so thus, on top of the demand profits. I honestly don't know why traders have not gone nuts to support Torval, because that 5% goes up and up the higher Torval get's in the ratings. Yet Torval struggles.