1) S1 means "Selfed", which is different than saying "self-pollination". Only hermies self-pollinate.
2) In terms of diversity, it depends on the strain you start with. Is is true breeding? f1? f2? f3? If the line is stable, then the offspring should be uniform.
3) The "Selfed" seeds are not f2s...when you "self", you are inbreeding the line to itself, in other words, cubing.
4) "Selfed" seeds are NOT hermies...
"selfing" is the process by which a chemical agent is used on the plant during flowering, to prevent female hormones from reaching the plant's flowers...So you end up with "female pollen"...Since the pollen source WAS NOT from a male, there is no male genes. So when the plant is pollinated with the "female pollen", you should have feminized seeds (female pollen (XX) + female flowers (XX) = feminized seeds (XX)...
Female plants produce male and female hormones. So by restricting the female hormones from reaching the flowers, it will take on male characteristics, but genetically still be female...
Theoretically, there should be no hermies...but in Nature, you cannot control such things...hermaphrodism is a survival tool...
Part of it is up to us to provide the right environment for our plants...because if we don't then feminized seeds don't work...
But there is one problem with "Selfed" seeds...and that is the possibility of recessive trait becoming dominant...