I don't see what use a 5* Finalizer would be by itself. If you're not at the point where you have Neg or Mal, and you're running Finalizer with your best ships, a star probably wouldn't help much and you'd be just as well served by Tarkin or Chimaera.
If you have a solid FO fleet to run behind it, then you can farm the challenge tier. If you are farming it just for SLKR, you're also working on FO so you can farm the challenge tier.
Spend those crystals on useful things and go after Neg/Mal for ships.