Interesting and seems to be well thought out.
Their 12 bore slug data can easily be improved with handloading, but is likely quite suitable.
Lyman's Shotshell loading manual has some good data.

The Canadian Made, "Challenger Slug" ammo has a 496gr. Gualandi DGS (Dangerous Game slug) in 2 3/4" ammo at 1,610fps.
The WW 3" 1 ounce Foster Slug running 1,750fps.
Both of these full sized factory slugs will put 5 into 2" at 30 yards, elbow rest on a table top - ending up with just a hole, form my fully rifled 24" Mossberg, with open sights.
The WW 3" has considerable recoil, the Challenger, less so.