all my fence lines, have wire running all the way down to the ground. so no use for me. but looking at original video you posted. and remember what i have looked at over the years "attempting to find a trimmer", that DR. trimmer, does not look good to me. the 3pt hitch trimmers for fence lines i do remember, had a much longer "guide bar", that to me would not catch on a post if you ended up to close to the post. that round disc DR is showing. seems like the posts will end up taking a beating errr "cutting" almost, result leaving a grove at bottom of post.
the couple trimmers i do remember "flipped around" the post. to make sure both sides of post was cut, and then reached around a bit more to cut all 4 sides of the post. (no need to take a pass down one side of fence, then go around to other side of fence and make another pass.
i do not remember the name / brand. it had a simpler "spring" action to go around posts. and it simply followed the ground. no need for tilting it manually or through hydraulics.