A very interesting design and fascinating piece of cycling history. Thanks for sharing it with us.
I think it must have been quite awkward in use though.
Considering that the drawing in the patent application doesn't show a coaster brake fitted, you could imagine that a "coasting peg" (as previously, separately discussed) fitted to the downtube would be very useful as a support for your toes whilst using your heel to operate the brake.
Otherwise if you used your toes/ball of the foot to operate that lever, your heel would've been very, very close to what may be a rapidly spinning rat-trap pedal, especially on a downhill; and impact on the heel from such a thing definitely hurts, believe me.
Of course, it could be an armless type of coaster, or an early ND device mounted on the drive-side of the bicycle in the patent illustration, who can say, but the application wording does describe "back pedaling" with your drive-side leg.....
...I can't imagine trying to 'leg-brake' using only your right leg whilst operating this system with your left.
But then again, the angle of the operating lever in the photo of your great-grandfather is very different to the angle shown in the patent application, which suggests that the device has gone through some process of 'trial and error' in use before he was happy with it, or maybe that he only had a smaller diameter braking disk to utilise when he made this.
I can't imagine he was too happy when coaster-brakes were starting to be introduced around the same time, or very shortly afterwards.
Anyway, enough conjecture on my part.
I love seeing and learning something new on here.
Keep it coming.