If your looking for a good ball mold I've been using the Russian Svarog molds, cast a great ball, I've found the .678 mold to be the best accuracy wise and it cast a 1oz ball.
Sit that on a 20ga felt cushion and it's easy to load and shoots great.
Their match slug is pretty good too, kill great as well. But the paradox mold that cast a slug very similar to the one you posted the link to will do a brilliant job.
Last I checked they had a good selection of those in 20ga options.
I'm thinking about adding one to my collection.