That's ... debatable (well, debated in one of my troupes anyway).
We ended up having a verditius create a few wand with the Bellum effect enchanted into them.
Quick and easy, and all of our future apprentices would be able to use them. We even managed to make Bellum a fixture at tribunals, meaning magi would bring their apprentices to tribunals to have them compete.
Or if a stress die is to be used that it gets at least one botch die, and therefore the odds of creating a piece of boiling hot glass that hits you in the face rises rapidly.
That+long term fatigue is obviously going to kick in. Just because something is non-fatiguing to do for 6 seconds, doesn't mean it's non-fatiguing to do it for an hour.
As an SG, I don't like to wield the club like that. I prefer players have a come to Hermes moment and figure out that kind of gross (obscenely large) behavior isn't really acceptable. No one spell should allow one to practice finesse better than another spell, and one shouldn't have an expectation that it could be turned into a money-making exercise. Attempts to do so, despite my insistence that I'd rather they not might see something like this happen, but man, I'd have to have gone through a litany of reasons on why I didn't like it.
Now, if you and I discuss your character's intentions, that this is what the character wants to do, and you, as the player, don't have any expectation that your character would get a result that they want, and are giving me some room to create something interesting, that's completely different, and I'm less likely to blast the character's face with molten glass and instead probably convene a special tribunal where the character is brought up on charges for interfering with mundanes because he had to dump all of their commodity on the market, bringing ruin open his sodales in the Tribunal or even other Tribunals...
If you are rolling a bunch of stress dice, what happens when you botch?
A sandstorm, obviously.
I don't see it as wielding a club. It's the logical result. If the player was somehow unaware of this risk I'd tell them, but it's a pretty obvious one: Roll tons of stress die and eventually you'll botch. And botching is bad. It's not just "nothing happens" it's "something bad happens".
A one-die botch is roughly equivalent to a minor wound. So you might burn yourself, or cause some other trouble. You won't be struck blind by molten glass, but you will have caused some problem that adds botch dice to your pool. A two-zero botch is explicitly equivalent to "struck blind" according to the rules for Hexes, so that's a plausible outcome at that point, although I'd assume the blindness was temporary (heals as a light wound probably).
I'd happily let them do it calmly and safely and roll no stress die. But if you declare "I'm taking chances because I want to make some masterpieces" then you're taking chances.
How about if they have Cautious with Finesse and the spell is mastered, effectively no chance of failure? It becomes a bit harder to justify something bad happening as a result of the spell, and you have to pursue the logistics of the situation as contrived by the player. There are worse things than having a heavy would due to getting blasted than melted glass, and defending yourself at Tribunal is probably one of them.
I wouldn't allow someone to say "I'm taking risks on purpose, but I'm being cautious about it". Either you're taking risks or you're being cautious, not both. The virtue represents something, it isn't a purely mechanical factor.
Now you may play differently, and be happy to allow "cautious with" to represent "I'm really good at taking risks"; that's fine, but it's not my style :p.
They're still rapidly spending long-term fatigue. The logistics are imposed by the world, and in-world casting non-fatiguing spells is non-fatiguing when you're doing it for a matter of combat rounds. (So, at the longest, about a minute).
Sprinting isn't even very fatiguing when done for that length of time. Certainly 6 seconds of sprinting for an athletic person counts as non-fatiguing. (otherwise no-one could sprint for more than 30 seconds)
Sure, but to get to that stage first you have to overcome the other problems in your way. I'm not coming up with these problems to get in the way; these are the problems that I see as already in the way. I'd have to deliberately ignore them if I wanted to skip to the Tribunal issue. And if I deliberately ignore the issues once, I'm setting myself up for problems later on.
I'd far rather let the players try and work around the issues that exist than just pretend those issues don't exist.
You and I are largely in agreement. I was playing devil's advocate. Cautious with finesse does remove the risk of botching with finesse unless you have more than 2 botch dice, I'm sure we've had arguments with players who say I have X and I shouldn't have to deal with your limitation. Heck, I've done that argument as a player. 
I don't pretend issues don't exist, I do say that they have somehow managed to overcome the logistics issues. If players want to take the rules and min-max them 12 ways from Sunday, well, I'll just trump them with story, if I have to. I'd just rather that they come to an understanding of what's reasonable, or at least accept that my idea of reasonable is different from their idea of reasonable, and be able to find some level of common ground or compromise. It's far more interesting to me to have a Tribunal story than to have someone get their face melted off because of molten glass.
If the spell is mastered then when you are in calm situations you roll a no-botch stress die. So yes, careull with could still aply, since the stress die comes from mastery instead of a stressful situation.
Mastery doesn't give a stress die on the finesse roll, it gives it on the casting roll.
True. On the other hand, a finess botch is far less of a problem than a spell botch.
Seven League Stride suggests appearing in a wall if the finesse roll is botched (part of the reason my characters skip this spell if they can, because The Leap of Homecoming doesn't have such a requirement). Translocating into a wall would seem to be a pretty big problem.
It suggests it as a possibility, presumably for a bad botch. It also seems to indicate it not being lethal. Considering you have to roll a finesse botch to even land anywhere other than where you intended, I certainly wouldn't expect it to be a single botch. If you botch the spell, you get warping plus the spell does something other than what you intended, and more powerful spells should have more powerful botches, meaning a botch on the spell could pick you up and slam you into a hillside. Basing off PeCO guidelines, this could result in instant death for the person being moved. So yes, I would say the botch on spell casting is still worse.
With regards to craft magic, a botch on fines does, presumably, the same as what a craftsman could do with a botch, which is ruin the materials. With 1 botch die that's a 1:100 chance of ruining the materials. Not bad odds really...
I'd give the storyguide a fair amount of latitude on what the botch does. Magical work is faster and more productive, but that also should equate to faster and large botch results. Like using an computer to make calculations instead of by hand. The computer will make a mess very quickly if there is an error.
A botch isn't "nothing happens" it's "something bad happens". A single botch is explicitly equivalent to a minor Hex (and to a minor disease).
Ruining the materials and wasting a significant time crafting is "something bad happens". It's a reasonable result for a minor hex to produce.
Ruining a small bit of sand on a botch to turn sand into glass is "nothing happens". It costs you six seconds. A minor hex would be more significant than that.
Botching with finess would ruin materials faster than crafting the slow method, but the finesse is not the spell. Unless you decide that you produce something accidently obscene instead I really don't see how bad the finesse botch could get.
In Against the Dark, pg 61, describes a magic item
So a magic item could be made to practice Finesse rather than making sand castles or lots of wooden chairs.
Well, you're moving objects magically at high speed, and heating sand to its melting point. That's what success with the spell means.
The finesse roll is you trying to form that high-speed molten sand into a finely crafted glass object. In six seconds.
So you're moving molten sand at high speed, and you can't see how that could go disastrously wrong?
Botching with such an item used by grogs to get lucky with their finesse roll could result in the classical: "the item is destroyed".
Double or more botching (which would not be so uncommon since enervation arise quickly when you repeat the same without comprehension) could include : the grogs turns the sand in lava and suffers wounds.
Magic is not something you can/should turn into industrial processes, because it creates too many incoherent, in universe, flaws of the game.