Swindler is an obvious comparison. there are some key differences.
Swindler is especially good early since the chance of hitting Coppers (into Curses) is higher or you might hit a critical card your opponent bought early (say a Witch/Mountebank into Duchy).
Of course it can turn Estates into Estates and that's awful, so it's rather swingy but still good early on.
During the mid/late game if you're turning Silvers into Silvers or Golds into Golds, that's not great, other than the fact your opponent has to wait a shuffle to draw them.
And if you're behind and turning Provinces into Provinces (or, my personal favorite, Peddlers into Provinces) well that's just sad.
Barbarian seems stronger, but note that your opponent gets to choose the replacement, not you. Yes, often it will turn Province -> Duchy -> Estate and Gold -> Silver -> Copper, but if there are special $5 Treasures like Idol, Relic etc. it becomes less hurtful to trash a Gold and likewise for VP cards if there are kingdom VP cards like Nobles, Harem, Island, etc.