I know several people who use them, attached to a custom base plate, to tow a Miata. They work well.
The major upside is that they can usually be bought for less than $100. Combined with a $100 custom base plate, one can usually be towing for ~ $250.
The major downside is that because the arms are not length-adjustable, the towed vehicle must be perfectly aligned, left-to-right and front-to-back, for the coupler to attach to the hitch ball.
This alignment process usually takes 2 people.
I used a custom made, rigid arm, tow bar (below) for 5 years and 35,000 miles.

Tim