Nice one - but it if the post is too old or a bit rotten, don't attach your tow line from the tractor too high up on the post. It might multiply into two posts!
Never used those, they rot quick with all that buried open grain. Made an 'H' frame and cross braced with wire. 2 posts sunk 3 foot give a solid anchor to work from.
Why would put a breast plate in and a stay the foot at the bottom will stop any lifting or twisting action also use a swinging foot as they are far easier to place in and requires far less digging