I had help in setting the posts from my landscape contractor. His guys were fast (a day versus me taking longer). I had 1x4 bracing on site but he said, no need. Their method worked perfectly. The posts are aligned and plumb. Great job.
He said he had a job once to set 300 posts. No way to brace that many in a cost effective manner. Just a string, a 4’ level, concrete and a tamper.