We always used balast and concrete, we would mix 4 to 1 ratio then put it in dry. We used a sledge to "tamp" the holes basically compact the ballast. Then we would just water the holes with a watering can before we left. I was taught by an old school that's how we learned to do it
I put a post in the other day, used blue circle post creat. Post was perfect, over several hours the post moved as the post creat fully hardened. Luckily it was close to the garage and was able to wedge some timer in-between to bring the post back to vertical