There are plenty of cards you don't want to play early, I don't think this makes it a bad card.
And there are also plenty of cards that can end the game in your favor if you've got a 4-3 Province split.. Salvager being the most obvious.
The effect seems pretty weak, though. If it's a card I really like, gaining another one plus a curse isn't much of a punishment - and is sometimes a gain. If it's a card I'm "meh" about, losing it isn't much of a punishment. I'm thinking it's Swindler-ish in value.
It would also slow down the game, especially with 3-4 players, because it involves a choice made by BOTH the attacker and the victim. Are there any other cards like that?