Perfectly sound.No public analyses has ever shown it to be refuted allthough people often think so.Makes many appearances in corr chess scoring many victories.
It's great fun to play but not at all easy,if your opponent knows what he's doing you'll face a tough fight.
Often Black will decline the 2nd pawn after which play can transpose into the Göring gambit which is perfectly sound as well.
The Capablanca defense (3....,d5) is troublesome for white(imo anyway,cause I don't like facing it) but by no means a refutation.
6.Nf3 here Black has several options but the position is considered equal.
The Danish is great fun to play but it's dangerous.You can destroy your opponent in great style but at the same time one little slip and it's you who's blown to pieces.