Not particularly dense and not evergreen.

I wasn't looking for evergreen because I hardly ever go outdoors during the winter. I will use them in other plantings.

Yes they are supposed to be seedlings, so we will see. I ordered 10 buttonbush and 10 pawpaw trees. They come in February. I am also looking at making some buttonbush standards.

They are something of a one-season wonder, with the flowers attracting many insects in summer. Around here they only grow in really damp spots - wet open woodlands, pond margins and similar sites. I will planting some here, but in wild areas that I am rehabbing from vehicle damage, not in a garden space. Missouri Botanical Garden has a number of photos including some planted as a hedge that might help you make up your mind as to their screening effectiveness.

Thanks for the link. I probably won't use them as a screen.