Good point, we don't use those lab rules, so I forgot about them.
But I think 0.81%, while a reasonable risk for a one-off, is enough to be an important factor in a repeated pattern of behaviour. If Vis is how you're learning, you'll be rolling a lot.
Thanks for the maths. This is what makes it hard for me to accept that there isn't a mountain of tractactus. I think many magi would want to go past 20 in at least two arts. To get from 21 to 25 is 94 XP, so on average 10 seasons. That is a 34% chance to warp at least once. Too dangerous for the return. In a low aura covenant, even more so.
Any one use item, such as the "Root" summae, or a tractatus, it seems illogical not to share them for profit. Imagine 4 covenants get together and make a deal that the covenant must make 5 tractactii available each, then every year, 1 more tractatus joins the pool. For a 5 magi covenant that would mean once every 5 years a magi would need to write a tractatus and have a huge pool to choose from.
If study from vis was 1 pawn per 10, and the die roll was aura + pawns + stress roll, it would be a little more viable to study from vis.
I think people here seem to emphasize the problems with learning from Vis, and seem to disregard the benefits:
Sure getting some kind of Vis is easy -- spend a single season in the Lab. Fine. But getting a particular type of Vis? Technique Vis? High demand (like Creo and Corpus) Vis? No way that is easier than simply getting another mage to instruct you at SQ 15.
Sure, I understand this is saga dependent -- there were circumstances that were engineered by the story to do things the way you did. But a cool thing about books is that they can be used more than once, and by more than one person -- once the Vis is used, it is gone. Once your Covenant has a Creo Root, or a couple Tracti, then every mage in the Covenant can get to Creo 5 in just a season or two.
For sure that my case was a bit of a edge case, but we had an Aquam Vis source, and none of us specialized in Aquam, and in the 10 years we've been there, we stockpiled a good amount of Aquam Vis, so it wasn't a problem to learn it from Vis.
Some Arts might be harder to have the correct Tech or Form Vis around, but it's can be easier to either attend the Summer Fair in the Alpine Tribunal, held every year, or ask a Redcap to bring you a few pawns of the right Vis in exchange for Vis you might have surplus of.
In Sagas I've played in, if you bought a book, it usually took about a year or more for it to be delivered, since covenants usually didn't have a copy available, and they needed to have a scribe, binder and illuminator dedicate time to copy it, and transport takes time. And books aren't cheap. While the roots are cheap at 1 pawn, most books cost much more than that, and we've even paid 28 pawns for a single book.
I'm not saying studying from Vis is the easiest, but sometimes it's necessary, and it has the upside of potentially earning you lots more xp if the die explodes.
This is at most a marginal benefit. The stress die averages 5 (5.5 on a 1 reroll because 0 counts as 10).
The doubling adds about a 25% increase in expectation value for the roll (210% + 41% + 80.1%…). That’s an increase of 5.5.25 = 1.375 in expectation value.
It’s not that that is nothing, but it still leaves studying from vis averaging less XP per season while risking Warping and Twilight.
That will be a saga choice, but rationally the supply of tractatus that are equals to or better than studying vis in an Aura of 3 will be arbitrarily high given the rules and a 450 year history of the order.
After all, if you can write a tractatus at quality 8+, someone out there will be willing to give you 5+ pawns of vis to avoid the risks of studying from that same vis.
Studying a significato has all of the chancy upsides of studying from vis, but no vis involved so no botch/Twilight risks (... depending on what event you're studying, I suppose). It's in a bit of a wall of text in Covenants so may be easy to miss, but it's surprising that people don't make seeking out significant magical events a priority for their magi.
My Verditius rolled a string of 1s studying a significato and unexpectedly found himself a Creo specialist after gaining 128xp for the season. He could do it in his own laboratory (since it was his familiar he was studying), but if you had to travel to see the event that would give the fallback of Story experience for the season instead if your significato study roll was somewhat lackluster.
Thanks! I had forgotten that, and, since it bugged me that you couldn't learn ignem while studying a Dragon, I was in the midst of writing rules for that 
The rules have a Significato as being exactly like studying from specific Vis; with two important distinctions. 1} there may not be any warping or twilight from botching; and 2} the Significato counts as a certain number of Vis. So it is possible that a Significato may not count as enough Vis to qualify for your mage to improve their Art, and it does not seem like more Vis (over and above the Significato) may be consumed.
Realia seem more generally useful; but a mage will want to study as large a collection of Realia as possible.
That would be 1,1,1,1 then 8. So a 1 in 100 000 chance. I appreciate 1,1 then 2+ is decent, but that is 1 in 111, so again pretty marginal.
Pointing out this edge case only shines a brighter spotlight on how unlikely good results from vis study, or significato are.
Well, if the significato happens to be a creature with Might we have an idea how much vis they're "worth" so I use that as a rule of thumb for how many pawns studying one would count as. Flambeau archmagi would be seeking out the death & hatching of a phoenix, not of a sparrow of virtue.
I'd probably use the equivalent Magnitude of other spectacles as how much vis they'd count as for significato study. 1-pawn significatos should be fairly trivial and fairly common, I think. The impressive events should count as enough pawns of vis that they should be attractive to most magi.
As you said that one of the objectives was to have simpler rules, why did you keep two book types?
What do you think of an even simpler version, where there is only one book type, the tractatus that you describe, and a tractatus can be read multiple times?
It would avoid the need of keeping track of which books have been read by each character.
Maybe one could decide that, if the Learning Total is negative, then the Source Quality is 2, independently of the Book Quality, which is the same amount of xp than exposure, but with no risk because no other activity than reading.
As I wrote somewhere along the topic, if you look at the first post there is no restriction in the proposed ruleset about reading a tractatus twice.
And the summae I propose are just a collection of related tractatus, that were written to complement each other. Reading several of the one after the other gives you a small bonus to Quality after the first season, to reflect the fact that they reference each other, which makes things easier to understand.
As for reducing the SQ to 2 at both ends of the scale, that is certainly something to consider.
I find vis study to be fine. Not sure why you guys are gaging vs an Aura of 3. Vis study does not require a lab so you can go Aura hunting and most Magi will have access for a season to a high aura. You might even want to do the Hermetic Pilgrimage of Aligned Auras (RoP:M p.16) which takes you to not only high value auras but they are doubled for specific arts meaning you can hope for an aura of +16 for a given art and study it for a rewarding season.
W
High Aura provides a small SQ bonus to 'Studying from Vis'. but it also increases the chances of (and severity of) botching. I'm not sure it is worthwhile to seek out a high Aura.
One thing to consider is maybe changing how the stress die works for Studying from Vis; instead of 'Each result of 1 on the die doubles the multiplier, and allows a reroll -- the multiplier applies to the final die roll' change this to 'Each result of 1 on the die doubles the multiplier, and allows a reroll -- the multiplier applies to the final SQ'. The chances are still 1 in 10 to have a roll-for-botch and 1 in 10 to roll-for-exploding-doublings -- but at least the Aura (and other modifiers) gets multiplied along with the die total. It makes the stress die a little more palatable.
At this moment, the first post says:
I am not certain that a high magical aura would cause an increased botch chance of studying from Vis.
If I recall correctly the number of botch die would increase based on the amount of Vis used. The aura would only add botch die if it were not aligned with its use. (E.g a mage Studying Vis in a Faerie aura rather than a magical one.)
I also don't believe that other modifiers are doubled when you roll a 1. Only the result of the stress die is.
The covenant aura is a safe location. For that reason, I think it is a fair default.
Even if you took the Aura up to an 8, the average from a season of learning from vis is around 12.4, which is marginally better than what Covenants says is a common tractatus (11) but comes with a substantial risk of a botch.
I was in the same boat as you. I might be recalling the conclusion wrongly but as per corebook p.183 "For each point of aura rating, roll an extra botch die." & the conversation below, I think the ruling was you add the botch dice.
W
Learning from vis is not experimenting, which is the only activity I see that adds the aura to botch dice.
Unless there is a rule somewhere that I’m missing, of course…