IXC fanboy here.
Yeah they are big but carry so much torps and fuel that it's worth it a 100%. The boat only needs a skilled Kaleun
who is not going 'rambo' on convoys, using it like a PT-boat..
(A CrashDive hint, don't try to CD imidiatly, first hit flank and then CD when the speed is maxed, also, don't turn while CD'ing.)
Oh and btw, they look very impressive! Any IX Kaleun would agree with me that there is not much else that looks so awesome as seeing a IX plow tru the Atlantic storms.
So sum it up: IX boats are for Kaleuns with balls!