How do the sirens lure travelers to their destruction? How does the danger posed by the sirens compare to that posed by the lotus-eaters?

The sirens lure men to their death by singing to them. 
Their songs are so beautiful that the men are unable to resist coming over to
them.

The danger from the sirens is much greater than that
from the lotus eaters.  However, they are both equally dangerous if your goal is to get
to your destination.

The reason i say they are both equally
dangerous is that they will both keep a traveler from getting home.  But the sirens do
it by killing the traveler and that seems rather worse than just staying with the lotus
eaters for your whole life because you like eating lotuses.