lots of good info here! Thought I'd throw in my own two cents (for what its worth
)
speaking in terms of F1, F2, etc through F6 being the most stable, germinating seeds that are designated as generations F1, F2, F3 will produce variable results, the more stable genetics won't have as much deviation as the earlier ones. You may get two or three deviations (sometimes more) from a hybrid that's specified as anything less than an F3. If you want truly stable genetics, don't waste your money on anything less than F3, if you can help it.
To give you an example, I just harvested two plants from the same F2 seeds I was given by a friend. It was crossed with GDP (Granddaddy Purp) and GC (Green Crack). One plant was done a little bit sooner and was a somewhat speedy high like the GC and the taller took an extra few weeks and was spiked with purple and blackish leaves (traits from GDP) and gives a nice full body high.
The smoke from both plants was pretty amazing, so I'm not telling you never grow an F2 or less, just know you will most likely have significant variation.
For more info and specifics, you can check out this old thread,
@fdd2blk explains it well...
https://www.rollitup.org/t/diffrence-between-f1-and-f2-f3.36545/