When I lived in Africa, every avocado was grown from seed. There wasn't any consistency in what you would find in the market, so it was a matter of quantity, not quality. Yes, you can grow from seed, and yes, there will be a fair number of them that will actually be fruitful. But will you get decent fruit that you'll want to eat? Further, you could wait 5 years and still not get anything. It's a crap shoot.
If you have
land and lots of time and space, then it seems like a great experiment. But if you're limited for land and time, it makes a whole lot more sense to buy a grafted tree from a tried and true cultivar.
"The rule of no realm is mine. But all worthy things that are in peril as the world now stands, these are my care. And for my part, I shall not wholly fail in my task if anything that passes through this night can still grow fairer or bear fruit and flower again in days to come. For I too am a steward. Did you not know?" Gandolf