Product review (4 stars): Does the job - but requires extra work. Product picture is inaccurate.
The coupler I got is the newer type that has a metal insert around the center hole, and the rubber part is red not black. The product picture depicts the older type of coupler.

The newer type should be better because of the metal insert - the all-plastic part in the older type was too weak and failed. There is one issue wth the new type though: the metal insert has extra material that I had to file off in order to make it fit the shafts of the motor and of the gearbox.