Legal is Supersprint or Eisenmann. Remus has issues now very hard (NOT Impossible) to xfer ownership of exhaust due local distributor closing shop
Regarding Remus ,someone said that LTA will help in transfer.Just need to write in allegedly.
Your butt won't feel a difference with an NA even after a tune.
And i won't operate on a stock xos.
Sometimes, you may think there are plenty lying around but the irony is when you really want one, you cant find one. So u may want to get a used system.