I have noticed with a lot of things to do with astro piers, everything is way over engineered for its purpose. J bolts are usually recommended for installing heavy machinery that vibrate a lot, where a normal fixing ie dynabolt would eventually move and crack the concrete.
My pier is fixed with screw in concrete anchors
https://www.bunnings.com.au/ramset-1...nchor_p2260296 . These anchor screws apparently have double the hold down capacity of dynabolts. Wet set threaded rod would be inherently stronger than a dynabolt or chemset bolt installation.
An M12 ramset bolt will hold about 400kgs in low strength 20mpa concrete and I think a solid fixed m12 bolt has a shear capacity of over 1 tonne, so multiply that by 4 and your base will support over 1000kg's.