Let's review a bit what Torrent of Power of power does:
- If you don't spend any charge, you only get a icon, making it strictly inferior to Unexpected Courage
- If you spend one charge, you get a icons boost, making it slightly better than an Unexpected Courage or a Guts in terms of raw icons, but the additional may not be relevant (so it would not be better than Unexpected Courage in this case) and you don't get to draw (so not overall better than Guts)
- If you spend two charges, you get which starts to look like a huge boost, but at this point the icons start to be less relevant and more overkill
- If you spend three charges, you get a boost which would probably pass any test, but now we are looking at a really expensive one-shot test pass tool.
Contrary to the above review, I believe that this card does not justifies the inclusion of fringe spells. Fringe spells were that way because they range from bad to barely average. Now, combining these spells with Torrent of Power sure is a combo, but not a particularly impressive one. Say that you add Alchemical Transmutation to your deck in hope to spend your charges on Torrent of Power: even if you happen to draw both at the same time, it is unlikely that you will need to spend all the charges just for a particular skill test, and will be left on the board with a useless Alchemical Transmutation. In other words, you will have drafted into your deck Torrent of Power (maybe instead of Unexpected Courage) and Alchemical Transmutation (instead of any card that is actually good) just to get a single boost on a single test. And if you don't draw them at the same time, they are actually useless. Worse, Alchemical Transmutation could just be sitting here, clogging you arcane slots (and if you are running Sign Magick for the sole reason of using Torrent of Power, you now have 1 additional card to find to get your combo going, and the price of this card is added to the price of the combo)! Cards that are bad alone are rarely good when put together, and when the combined use is not particularly strong it is just better to skip these cards.
Besides, the fact that you have to spend charges from an asset also means that you are essentially paying to power up Torrent of Power. If you use a charge from Rite of Seeking, you are using one third of the charges of a spell that costed 1 card / 4 resources / 1 action to play, or in other word you are paying an additional cost of 0.3 card / 1.3 resources / 0.3 action to get an additional boost. Compare this to Unexpected Courage that would additionally cost you 0 card / 0 resource / 0 action to provide you with a boost, only missing out a sole icon that may not even be relevant to the test you are trying to pass - not a great deal. On top of that you are now out of one charge on your Rite of Seeking, and Mystics don't like being out of charges on their spells because that's what they use for most of their skill tests, and are essentially sitting ducks without their them.
The nail in the coffin is that you may in the end just fail the skill test (maybe through a ). Yes, you may fail any skill test, but failing a skill test on which you haven't committed anything is vastly different from failing a skill test on which you have committed 1 card and 3 charges, or just 1 card if you had used Unexpected Courage or Guts instead.
So, is Torrent of Power that bad? No, but it's situational, and has to be played correctly. It is best used on assets with charges that are situational but good (meaning that you probably have charges to spare), cheap and have a lot of charges (meaning that spending a charge is overall less expensive), like Clarity of Mind (3), Mists of R'lyeh, and Grotesque Statue (though this last one rarely has too many charges). So instead of playing bad cards and hope to get a value from them through Torrent of Power, you are now playing good cards that you can use to power up Torrent of Power without feeling that you have weakened your deck or that you have to wait for an incredibly difficult test to spend 3 charges to make it worth.
As for specific investigators, Torrent of Power gets better in an Akachi Onyele decks who has additional charges to spare and Spirit-Speaker for even more charges. It is also probably better in investigators decks that could use huge boosts due to their low base willpower (meaning that they would get more flexibility at using more charges), such as Carolyn Fern or Daisy Walker, tough it will be in tough competition for a deck slot as these investigators' job is not primarily to use Mystics spells and may simply not run enough of them. It may also be reasonable for investigators who use spells with a 4 base willpower, including most Mystics or Sefina Rousseau, but I'd probably skip this on Agnes Baker who don't really need such a boost due to her 5 base willpower.
In the end, I believe Torrent of Power is neither good nor bad, but mainly depends on your deck building which should probably include at least 3 different assets with charges to ensure a good versatility. if you want to draft this card, you should probably take the time to consider Guts and Unexpected Courage as well. Maybe you're going to end up running all three, maybe you're going to end up running none, but you should really weight your options depending on where your deck is going.