I think it's testable. Having an estate in hand means you made both a card worth 1 VP and a card with reaction utility (that may even have been used this turn) invisible. People pay 3$ for a Great Hall. This is a Great Hall that fizzles sometimes but has other utility. You won't always have an estate in hand of course and that balances out its versatility.
I think it's probably still slightly weak, but I wouldn't call it useless. And I think testing is necessary to ascertain which of the abilities needs a buff to get it where it needs to be. Probably just a +buy tacked in somewhere. This card becomes even cuter with +buy, then it comboes with itself during an estate rush.
I have to agree that Duchy gain is not a good idea. There's a crucial difference between Tunnel and a Duchy gainer - Golds massive Gold gain doesn't 3-pile and gain VP at the same time.
Though I think it should be tested as-is first, one change I would suggest is switching from Trader wording to Watchtower wording. That allows it to three pile faster by trashing curses, and lets it get along with Ironworks well (Donald ruled that Trader wording does not allow Ironworks to bestow any extra benefits at all ever
).
Using this card in conjunction with Witches to make your opponent gain all 10 curses is probably rather fun and effective though, so definitely test it as is first.