Yep, duck loads. I'd use the 6s for any size ducks and the 4s for geese. Both would work I'd think.
Hevi has been known to get "creative" with their marketing claims in the past. I think this is shot that has a density of 12 g/cc. True Tungsten is 18 g/cc. That's used mostly in turkey hunting with very small shot (8 or 9).
The OG Hevi shot was around 12 g/cc if I remember correct and people raved about it. I never shot any of it. For $50, this probably isn't a bad price for what you're getting and in today's market, but it's not for me. The slight increase in performance isn't worth the vast increase in price. YMMV
Edit to add: you asked about 20 gauge loads and I do think these high performance loads do make more sense as you go down in gauge size. Still have to know what your normal ranges are and rather or not you can put shot on the birds. A body can miss with anything and it hurts a lot more when it costs $2/shell.