How bad is it? It's the nadir of Hollywood propaganda films.
Should you see it? Sure. It's tackiness is enjoyable.
I didn't include "Red Nightmare" or some other propaganda disguised as storytelling films, but this one is enjoyable on its own merits. Gangsters, offered a $1,000,000 bounty on Hitler, get dropped into Germany. Hitler's moustache gets shaved off to show a scar that proves he's not a double and then people who've known him for years no longer recognize him - and execute him (then a double apparently replaced him for the duration of the war). The dialogue in this is often laugh out loud funny.