I built a similar one the other day using the same cords. They are so gentle that you can put your hand right in the spinning fingers without discomfort. Any suggestions on an optimum speed? I have been running mine with a Dewalt drill/driver with a very broad speed range available. I don't have any test subjects to test it on yet.
Couple thoughts: First, you should mount the drum itself between a couple support blocks so all that weight isn't cantilevered off your drill chuck. It might be ok to do it like you have it, but the engineer in me cringes. I also use double nut arrangements and flat washers to position it between the blocks with just a little wobble room. It should reduce shock loads on the hardware and on the drill itself.
Second: lock washers are your friend. If you use good hardware and spin it the correct direction you should be fine.
I am designing a drum style plucker right now that should end up costing midway between a Whizbang and a Featherman but hopefully work as well as the Featherman unit with virtually NO maintenance required. I am also working on a couple smaller home built units, one run off a drill, and one off a small 115v AC motor.