Had them out yesterday. They get hung way more than my slinky weights. They held up to the rocks well, and catch more water making more hydrodynamic drag. I was also used mono and not my normal leadcore set up. That also accounts for the extra drag.
I think a long narrow cylinder will be the way to go. I may have to make a mold of some kind and buy the additive that makes this stuff pour easily. Therefore make more of a pencil weight.