While I have SH4 installed for my US subs careers, I definately have abandoned it for U-Boat games for now. The main reason is that I use manual targeting, and have developed my own mod to have optics and TDC in the periscope to my liking (The mod is available for NYGM and will soon be for GWX 3), and currently I'm unable to port that to SH4 because of the peculir way things work in that game -due to the newly added ability to change the game's screen resolution-.
The interface for US submarines is good enough, the stadimeter is flexible, the torpedo settings can be done from the periscope via the TDC sub-page. But in the U-Boats you simply can't; the interface was directly ported from SH3 but with all the inherent limitations of SH4, including the re-scaling of the background image
which makes it impossible to put graphics in that image and expect them to remain consistent when screen res is changed. An example: A plotter in the game map created for 4:3 screen aspect ratio will no longer work if switching to 16:9 screen ratio
May be all this will get solved in the near future for talented modders, but till then I will prefer to stay with the U-Boats in SH3 and enjoy the US subs in SH4.