I did not compare in person, and only have limited experience with the Stehl. I do prefer the swivel deck design of the Stehl/Master Tow and others, just from a standpoint of the fundamental movements involved.
Any change in alignment of the dolly for/aft axis relative to the car for/aft axis will result in the dolly wheels pivoting forward on one side and aft on the other side. Simply allowing the car steer wheels to turn left or right will not account for the for/aft shift required.
Play around with a kids Radio Flyer wagon, similar principle.
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