im confused here, since an S1 is same strain x same strain, does that mean it be a more stable batch of seeds? I heard Caleb talking about a certain strain of S1's (i forget which) and he said something like itd be good for a breeder to pheno hunt through but not the average joe (because of the inconsistency between phenos im assuming?)
The stability of the S1 is determined by how stable the clone was that started it. Because a lot of Caleb's S1'S are made using heirloom clones or older clone only strains, there is no real selection for him to choose a more stable starting clone. If the cut he used to create the S1's is relatively stable then the S1 seeds should be pretty similar. Things start getting sketchy when you start an S1 program with a somewhat unstable strain on it's own, like the Chem '91, Chem D, OG's, GSC, this can double down on some of the mutants and stress-herm prone traits. So most S1 will have a higher amount of runts and mutants in each pack. On the flipside the best attributes can also be amplified, you can get an offspring even stronger than the parent cut.
Another note, there is some misconception that an S1 will turn out to be just an amplified copy of the parent. That is not really true and most people might be pretty bummed out to see the result is not really like what they started with. The best way I can describe the benefit to selfing a cut into itself, is it takes you backwards into the gene pool. If you S1 an extremely gassy OG, the offspring might put off a completely different smell or high from the other parent. So you can take something old and overworked, self it and the offspring will be completely different spread between the parents but still from the same family tree if that makes sense. It's almost like remaking a bunch of the original seeds that started the strain.
So because the rate of runts is higher, it can be not as fun to a consumer to sift through more seeds to find a truely unique plant. However if you have space and time to sift, you can find something extremely rare. You cannot find seeds of these clone only strains like Chem 91, OG kush, Purple Urkle, GSC, ect ect. But with the selfing method you can find seeds and new phenotypes within them all. That's why they are sought after for breeding/hunting.