You can usually get this set (also issued by Airfix) for much less than the RRP of about £40 in the UK. I paid £25 for mine. Other than the awful U-boat (I built this last month; it doesn't look too bad with some PE railings and weathering) the kits are fairly good, especially if you add photo-etch details (WEM produce quite a few 1/400 sets intended for German ships). So far, I've built the U-boat, two S-boats and a minesweeper; I plan on building one of the destroyers soon.
6 Schnellboots seems a bit too many considering they're all S-100s and there's a limit to how many different variants you can make (I'd rather have 2-3 and an extra destroyer or Torpedoboot), but if you have some scratchbuilding skills, the conversion to an earlier S-38 or similar is fairly easy.
I do prefer 1/350 to 1/400, but I can't really afford resin kits, and given the large range of subjects available in 1/400 the scale difference doesn't bother me too much.