Steve, this person has several brakes for sale as you say and many are different. The one you pointed directly to seems to have a ratchet and pawl mechanism right in the handle. You can see it near the top of the back open side of the handle. This would suggest to me that perhaps it is a locking drag brake for a tandem or perhaps just to prevent your bicycle from rolling away as you lean it against something. Also the construction says to me "heavy duty" and I have seen several similar brakes on the antique bike circuit, in fact I have a set of Mussleman hand brakes that look similar but without the ratchet.
Ray Homiski
Elizabeth, NJ