I never have either.
Ray, never seen a trailer coupler like that one before.
The design is unique but it isn't a very safe coupler.
It will work just fine for this rake but I would not have trusted it for towing a trailer down the road.
The gripping strength of the coupler is totally dependent on that thin strap that is wrapped around the front.
If that tension knob wasn't tight enough or the coupler got a good jolt from hitting a pot hole or something and that strap flipped up, the coupler would open up.
I enjoy looking thru old parts and accessory catalogs from the 20's and 30's and seeing all the different ideas they had back then.
Some ideas were good and others weren't so good.
I think a lot of small company's back then didn't spend much time or money on research and development.