In my mind, talisman is in a similar category as workshop and ironworks. Great for gaining multiple copies of cheap cards. Unlike the other two, it isn't played as an action and can't gain victory cards.
It's good in decks where you want a bunch of cheap non-victory cards, but in general this is not what you want, and I find myself ignoring it on most boards. If there are some very nice villages and cheap draw (Smithy, Envoy, maybe even Ironmonger), that I will be able to build an engine out of, Talisman can be a nice early buy to add components quickly. In a vineyards game, it can be very powerful for gaining extra actions. You might think a gardens deck would like talismans, but because it can't gain extra gardens, I think talisman is in general a very weak gardens enabler (at least by itself).
Talisman can, in rare situations, combo with bridge/highway/quarry to gain multiple copies of strong cards (more highways, Grand markets, etc). Again though, since it can't be used to gain green cards, at some point it just becomes a copper. If there are trash for benefit cards around, talisman can be more appealing if there are early game uses for it because you don't need to keep it around in the late game.
I don't consider talisman a particularly good card (by good card I mean a card that I would want in a large number of situations), but in some situations it can be strong.
I don't foresee duplicate being used in a similar way to talisman at all. Duplicate would make a very slow small-card gainer, not providing the speed duplicate brings to the engine player. I foresee duplicate being primarily used as large engine component gainers and in megaturns where you are turning in duplicates for duchies/provinces (when bridge and highway are around).