Well, they do have their uses.
They like noise, which makes them tend to hit the aft section of a destroyer or smaller escort, and in a few cases I've seen, they blow off a propeller, or damage the engines or propeller shafts of the escort ship, leaving it crippled and in some cases helpless.
After firing a few cuties at each oncoming escort I dive and run silent to escape, after awile you can surface and usually find a nice disabled destroyer that you can use your larger torpedoes on
I like them personally, but it takes some time to know when to use them, and how to use them in a way that suites your play style.