This card is unfortunately severely overcosted in my view. An asset that allows me, for an action, to do 1-3 testless damage against a non-Elite only, is useful in some circumstances. Big beefy non-Elites like Mindless Dancer, Eater of the Depths, or Deep One Bull can be taken down more easily with this pickup. But is this honestly the best choice of tech for those situations?
Let's go through all the negatives. First, it's exceptional, meaning you're paying 8 XP for a one of in your deck. With enough draw, this isn't inherently too much of a problem. You need curses to Seal. This is more of a problem as Mystics don't have much in the way of either Bless or Curse gen. Tides of Fate paired with a Bless investigator might be the way to go here. Now it is worth noting that part of the benefit of this card, presumably, is that it can seal curses for you in the short term. Unfortunately, this is hampered by the additional resource cost, where if you want to seal lots of curses, you need to pay a heavy upfront fee, and that too is another major negative as Mystics are one of the most resource starved classes. I think worst of all is that this exhausts. I would love the opportunity to spend several actions trying to manipulate enemy placement to get the best damage numbers possible, but the exhaust clause severely hampers this, and I genuinely don't understand why it's even on the card. Flute's uses are already severely limited by three(!) other things: resources, curses, and actions.
I would love to be proven wrong by this card. I think the movement opportunity and the ability to have enemies hit one another, or themselves, can be useful. But honestly, this card is severely hampered by one other element, which is the hand-slot. Traditionally, not a big deal in Mystic. But we just got Sword Cane this cycle, which costs 2 resources, doesn't require any curses, and gives you an immediate use when you play it. It also exhausts, but it allows you to evade an enemy or ping an enemy for one damage using willpower (not testless, but still your highest stat in Mystic most of the time). If you like directing where enemies are on the board, evading one and then running will have the hunters enter in and group together with the evaded enemy. If you want to do damage, 1 is not far off from the amount Flute would normally do, and it's perfectly fine to follow that up with a few Shrivelling charges for 3/5 health enemies. They're not exactly the same, but in practice I do think Sword Cane is a much more flexible card that has similar functions with significantly less investment. Now you do have two hands, so there's no reason you couldn't run both, but hand slots are at a higher premium than they used to be thanks to the taboo'd version of Scroll of Secrets being pretty good draw.
It's a bit of a shame, as I think this was meant to be the big Curse payoff for Mystics this cycle, but it misses the mark pretty badly in my opinion. But again, I would love to be proven wrong. There may be way more situations than I'm able to realize where this card just overperforms anything else.