In my limited experience breeding, i can tell you by far the are the most consitent and robust plants - health and gorwth wise. MAybe there's slightly more variation to it? but that's nice too from my perspective.
the f1 i made was superior to both parents in yield and had quality equal to both parents. the flavor can vary slightly from plant to plant but it's still similar. in this case it is a healthy mix of both parents, but i wouldn't expect that to always be true. just not how genetics work. it's not an average... it's a jumbling up and re-organization each generation.
When i grew some F1's from sweet seed it was also some of the most vigorous plants i've ever grown. Outcropping plants are highly susceptible to negative effects of inbreeding. Marijuana is an out-cropping plant. Even 1 geneartion has negative effects on robustness.
going forward i may breed a sistster with a sister, but the intention wil be to pair it up with something similar of a differnt genetic line to get the similar flavors and qulaity but with the excellent robustness of an F1
when i buy "R" reverse or "S' selfed plants, they are weak and shitty and you hope for a couple out of five to be good in my experience.
consitency? it's not worth it if it's a weak plant, in my opinion. your opinion may vary. I don't see "that" much more consistency either, lol.. seems like something that's been repeated so often without any verification but somewow becomes "truth" to the masses.