Nowadays it’s a wonderful gun to have with Naegling/Kaja sword. Not worth going beyond this point though, since there’s a lot better shooting guns. Naegling/Demersal Degen+1 or Blurred Knife+1 and this gun can rack up very nasty amounts of damage with Savage Blade spam.
Admitedly I've been out the game awaile, but assuming this has the same TP Bonus as the GK trial, I'm guessing this is the new Joyeuse-wielding COR's weapon of choice (if there isn't a better WS than Slug Shot with all the level cap increases)...