Cuties are nice mine are slightly modiied than default (speed) but from experience of useing them I have noticed they either do there job and disable the escorts or merchants props or just destroy the rudder or both and some times do nothing when they hit and the escort just speeds up and runs away.

I made many experimentations with cuties, and I only found them useful in a situation where you are below and sligthly ahead of a large convoy (preferably, large AND SLOW), and you do not have much time or means to raise your scope and plot a productive final run on a target.

In such a situation, you can simply drop your cuties along the path of the convoy, and they are almost sure to hit something. However, they're payload seems to be much smaller than a normal torpedo, so if it goes for the propellors and hit, it will likely only disable the ship. You will still have to go after him afterwards.