Gee, of course all of this is conceptural. There doesn't exist a non-mandatory cantrip trasher (except for, very losely speaking, Ratcatcher which has the disadvantage of having to be played at the beginning of your turn) but we talk about a hypothetical, the balanced price of a hypothetical mandatory or non-mandatory cantrip trasher.
The disadvantage of mandatory cantrip trashers is that it is either a dead card as you do not wanna trash anything anymore or a risky choice (with Lookout this risk decision occurs earlier). Upgrade is a quasi non-mandatory trasher as it remodels at the same time so it dampens (if you trash a good Action card you still got it out of your current shuffle cycle so it does hurt you but not as much as having to trash the good Action card) the disadvantage of being mandatory.
So, since all of the existing cantrip trashers are mandatory, I think it's safe to say that "normal" cantrip trashing is mandatory. Having it be optional would be a bonus.
Look, I'll lay out how existing and some theoretical cantrip trashers compare.
Basic+1 Card
+1 Action
Trash a card from your hand.
This would be a top-tier powerful $4 card, possibly too powerful to exist at that price. It would have worked at $5 (probably being just slightly below average at that price, which is still balanced). It might be powerful enough that it should cost $2, like Chapel. That said, it's probably more interesting to not have it at all, for the same reason there's no basic $4 Peddler.
Junk DealerThis is a
very powerful $5 card. It ranked 11 in the 2014 rankings, trending way up from its first appearance on the 2013 list. It could still move up more. Trashing is the big thing here.
The +$1 is a nice little bonus, but it is
only a bonus. The trashing is the main point. The bonus is consistent, always useful, but never spectacular. If you trash down successfully, you rarely want to play it late game (though sometimes you may take a risk).
UpgradeThis is also a powerful $5 card. It ranked 15 last year, trending upwards from previous years even as more cards get added to the competition. What are we to make of that? Two possibilities spring to mind, and I think the real answer is a mix of both. First, people are still underestimating how powerful trashing (especially cantrip trashing) really is. As players improve in their understanding of the game, they rank the card higher. Second, each subsequent expansion makes engines even better, so trashing is actually getting more powerful.
As before, trashing is the primary function. The TfB effect is a double-edged sword. When you trash Coppers, it is no bonus at all (unless Poor House is on the board, in which csae it is usually a major drawback that rules out Upgrade entirely!). When you trash Shelters, it is usually slightly negative (you may have to gain an Estate, or a weak $2 action that could interfere with terminal draw). When you trash Estates, it can be a really nice bonus (gaining $3 engine components) or a drawback (gaining Silver when you'd actually prefer nothing at all, which is not uncommon).
Usually the Upgrade bonus is worse than the Junk Dealer bonus, since the former is nothing ~70% of the time and mixed for the other ~30% (with the 70% nothing skewing up in the face of Curses, Ruins). Sometimes, however, you can get major work out of it. In the late-game, you can trash $4s into Duchies and $7s into Province. Sometimes you can even make ridiculous and amazing Upgrade chains (especially with Fortress and a $7 around). But this is uncommon. There's a reason why Junk Dealer ranks above Upgrade.
RatsThis barely qualifies for this list. It is a mandatory trasher, but it always gains another Rats (until the pile runs out). In effect, you are just trading (hopefully junk) cards for more Rats. Since your deck size never decreases, it doesn't play the same way as the other cantrip trashers. The Rats gain is a huge negative here. But that negative can sometimes be a positive, especially if there are other TfB around.
RatcatcherVery new, so jury is still out on this one. However, here are some salient points:
- The trashing is delayed by at least one turn. This is a huge drawback, slowing down the trashing a lot, especially in the early game.
- It is more likely to miss the first shuffle than not, since it misses if drawn on turn 4
or 5. It will miss even more shuffles as you trash down.
- You can only use it at the start of your turn. This limits your options.
- You can only play it every other turn at most.
- To be fair, it has a nice late-game advantage. If you're done trashing with it, you can just leave it in the Tavern forever (or until you draw that stray Curse).
- Even if it is extremely powerful, note that the $2 cost is the same as the cost for Chapel. Chapel is not a weak card. The $2 price point means that everybody can open with it without the 5/2 player being horribly set back.
Non-Mandatory+1 Card
+1 Action
You may trash a card from your hand.
This would probably be a $5 card. Early game, it is slightly worse than Junk Dealer and about on par with Upgrade in that the bonus (over the basic cantrip trasher) is nothing or neutral. Whether you prefer this or Upgrade will likely depend on Shelters or the presence of a good $3 action. Late game, this card is free to play. It doesn't have the same high potential as Upgrade, but it is consistently non-harmful. At this point of the game, it will often be better than Junk Dealer.
Set-Aside+1 Card
+1 Action
Set aside a card from your hand.
This is the card from the OP. It is almost certainly a
strong $5 card, easily beating Upgrade and quite possibly beating Junk Dealer as well.
Early game, this is on par with Upgrade as well as the Basic and Non-Mandatory trashers. All of these cards get nothing out of removing Copper, and are ~neutral with Shelters/Estates.
Now, the drawback. The -VP from Curses will still apply at the end of the game. But you still remove them from your deck, which is the biggest problem of Curses anyway. It's also partially off-set in that you will usually get to keep the 3VP of your starting Estates. And then there are all the games without Cursing, where those 3VP are just net positive.
But the bonus is even bigger than that. Since you set aside cards, you can slim down and still take advantage of cards like Gardens, Silk Road, Fairgrounds. Most importantly, you can set aside
other Victory cards, like Duchies and Provinces. You can maintain a slim deck even while greening, which means you can green much earlier. This is an
incredible bonus in the mid-game, and it effectively keeps you from ever reaching a late-game state since you'll just maintain your slim mid-game deck!