Scylla and Charybdis were called the Toothless Terrors IRL because of their armaments, which were smaller caliber than the other Didos, but managed to make them perhaps the best AA cruisers the Bongs built.

Dunno if Manjuu was going for it specifically, but they kind of live up to that name in AL. Both have personalities that send up a lot of red flags with their possessiveness, but neither actually do anything bad to you (though Scylla would oblige if you wanted that kind of thing). Charybdis will have panic attacks if she has trouble pampering you, and Scylla will occasionally do things to annoy you, but they never do any kind of harm.

Worth noting that Odysseus chose to go near Scylla when he had to choose. She claimed a few crew members, but that was better than losing the whole ship. Scylla is happy to have you be weak and dependent on her when you are alone, but she'll let you be normal in public. Charybdis will drown you in her love until you turn into the equivalent of one of those toy chihuahuas whose owners spoil them rotten.

TL;DR: Choose Scylla. She is safe, shitcan. Don't listen to the lies.