Before seeing Bills 400 lb mono rig, I was building them out of tuna cord which under normal fishing works reasonably well. However, as I often fish right on the bottom I found the tuna cord just ended up with a lot of breakage issues. Given the price of cannon balls these days (especially coated ones), I was looking for an alternative that was far more robust.
The issue with tuna cord that I encountered was it slowly rots over time and there is no real way to know when its done other than to replace the rig every couple of weeks. Tuna cord also seems to break fairly easily if you rub on any sharp rocks.
Whereas the 400 lb mono doesn't rot, and seems to have a lot of resistance to breakage if its dragged along sharp rocks. I fish over 100 days a season and by far Bill's rig is the best I've ever used.