I've done this and the seeds turned out good. its called a S1 or self pollinated first gen.
Depending on how good the genetics where to begin with will determine the output of the seeds your making.
I would not use any of the seeds you collect for any other breeding projects as its going to only go down hill if using the same genes over and over. if Mixing in some new genes then I would still opt for getting new seeds from the breeder vs using the off spring you collect.
None of the plants I grew from my S1 project went hemri and they all grew about the same. granted I used a name brand seed that was pretty good genetics to start off with.
growdiaries.com/diaries/129779-grow-journal-by-m0use
Good Luck!