on 24 February 2009
Both the 1st and 2nd volume are small books, relatively light on the information, don't expect anything even remotely similar to the Eberhard Rossler's books. Some interesting photographs, the central section has colour profiles of the major U-boat types, but overall it's a bit light on the information. Worthy of note, the section concerning the torpedos has some information that contradicts other sources, but it's hardly surprising, since to this day German torpedo technology in WW2 is a source of confusion, the nomenclature didn't helped.
Overall, it's something you read in 1h at most, a good general introduction on the U-boats topic, but could've been much better (joining vol.1 and vol.2 into a single volume).
Still, these are good introductions, but light on the information, with good (but small) quality illustrations and photographs.
It's not particularly expensive, so you do get what you pay for.
If you want a complete reference on U-boats, you might want to consider The History of the U-Boat, by Eberhard Rossler, but of course, at a much higher price tag.