I've crunched these guys out, done the grind, punched the frogs and noted it all down, I think I've earned the right to give an opinion worth listening to. Let's start with naming the problems and to delve into improvements.
Problems:
The activation method is derrailed, having gleamed the inner workings of how it actually acts in-game. Testing would have been nearly impossible if a certain someone didn't supply me the hex codes to shift, and it had taken over a year until I made a thread and made a call to action for anyone to have a clue of what they did, having been the man who ended up doing the action anyways. The fact it took a year to have any kind of concrete idea of what even one of these did is a travesty, and a sign of bad design. Most people thought it was a prank Styg, literally a gypsy scam, and that's not how you do a alternative feature like this.
Booth is present and static. He doesn't move, even if his location in the sewers can vary, but he's always there. Coral isn't. In fact I can barely ever find her even as I track all the way through every bar the South has to offer, making it a downright chore to even try and buy a charm after the early potential SGS/Junkyard location. I never found her after that and I have tried hard, and it should not be this hard to find a woman who wants to sell me animal body parts for good luck.
Her flavor is lacking and I can't help but to enjoy Booth more. While Coral has a nice picture to her and the whole thing of the spirits trapped inside the charms is kind of neat, it doesn't really compare to you having a literal mark of your achievements stapled onto your skin by a man who has dedicated himself to marking those that show by his doorstep, not even charging a charon for it. Booth marks you with the accomplishments of your journey, each perk thematic to the achievement or what you've done, and while in my opinion none of these are build key or super strong, I can't help but to try and seek him out and to have a little progress marked onto my character, literally in this case. It's the kind of flavor I love about Underrail and the South, getting tatoo'd by a mutant in the sewers, the guy himself marked with a damn Crawler on his skin, not letting his condition slow him down as he marks you with whatever you choose, a mark on your journey. Compared to a travelling saleswoman, Booth is just both easier to find, easier to get something you like and just so damn flavorful, how can I not love this guy?
The clarity of charms, or rather the absolute lack of it, is something I can't stress enough as a massive problem. It's understandable to have a mechanic not be fully data mined and fully comprehended and dissected in a game, it's another to have hidden modifiers related to belief of charms actually affecting it and by proxy, stuff like Coral actually cursing you if you call her out on being a scammer, which previous to the crunch I did, I could not blame anyone at all for. The fact the curse is hidden is god awful, as anyone unaware or playing as a first timer could easily just think "Ah, she's just fucking around and meant to be a scamming saleswoman, lemme call her out on it" and then get hexed ingame for his entire playthrough. It's not good at all Styg, and I'm not saying for you to show the 50 second charm buff, but good God, don't do this either.
You'll have noticed all of these aren't related to balance at all. Truth be told, I had to punch frogs 6000 times on some tests to find a different Styg but it isn't even about balance that I'm worried about. A minor buff to these would maybe be something interesting to consider, but the issues here push aside the actual number crunching from the sweaty Dominating optimization and focus on the issues inherent with the charms. Their presentation is strange, their effects cryptic, their flavour is lacking, their nature is hidden. People groan when they see Coral and don't bother with charms, they delete the Coral file so only Booth appears and if you sincerely want Charms to be not just a part of the game but a good one, here are my suggestions.
Improvements:
Make the activation method less insane. Make it so your charm vibrate or slightly glow whenever inside the activation period when equipped and to settle down when its over. This will make it clear Coral isn't scamming you and there is some actual shebang to it, perhaps only if you try to inquire and talk as much as you can about how they work and such so your "faith" is rewarded if you believe it to be better that way. Also makes them actually practical to use and not a complete meme to guess whenever they are even working or not, which is BAD DESIGN.
Make Coral much more static. I know she is a wandering saleswoman, but you can definitely do something like shoving her in Rail Crossing while the Faceless are there, then leave for Core city until the Cube is stolen and then to chill at the Hanging Rat until the end of the game, maybe sometimes hanging out in SGS or Junkyard again. Make her stay in some kind of "guaranteed" spot with a few different places to go to instead of having to go on the Dude Marathon whenever you want to talk to her.
Maybe make her more likable as an NPC? Having her with her own ghost stories and the like she tells the Player if he believes in the charms and wears them as they talk, some cryptic hints at stuff she's seen, monoliths and more, perhaps even a special kind of merchandise for a trapper in the know of the paranormal, like if you've seen the spooky rectangle or what comes out of it/Dom utility tower and she shares some limited merchandise bolts for a crossbower. She has some potential as a character honestly, so you can play with her being like a less grief stricken Katya and to give her own insight into things over a bottle of brew or two.
The hot spicy suggestion is to have her not be "either or" with Booth. Both can coexist and not cause issues in either balance or flavor, but in fact can coexist and make stuff cooler, a tatoo'd one man army kissing up his charm as he heads on out to the dangerous tasks he's given, praying for good luck with his progress marked on his back. That's beyond flavourful and having more NPCs like that in the South is something that's always appreciated, as good NPCs can sometimes make the world feel beyond alive.
I know development in Infusion is under way, but even if nothing gets done on the game we have now, which would be understandable, I just don't want charms or anything similar in design to be in Infusion. Even if you don't change anything within the code, please do change the design you have in mind, because Charms, as they stand, are bad enough people are diving into the files so they never see Coral again. That's a sign that something isn't right and that something needs to change for the better.