For a commercial growers, you do want a root stock and a scion graft. Scion is chosen to be a prolific producer but the root may not be as strong...

But for home grown avos. the single tree from the pit will be just fine. It will produce IF THERE IS ANOTHER AVOCADO TREE NEARBY. IT'S ONE OF THOSE THINGS WHERE IT NEEDS A COMPANION TREE.

My partners avocado tree was from a pit and it produced just fine. The tree can tolerate some mild freezing but that's about it. winter time high should be well above freezing.

Good luck