These three volumes are remarkably comprehensive and deserve credit for that. There are problems, though. Originally written in German, it has been translated into American. You soon get used to the liters and the fact that a hood is not what you first thought. There are some curious turns of phrase, particularly amongst the technical expressions. Also, there are lots of adjectival nouns. A pet hate. Nevertheless, it is easy to read.
One of the two authors, Jurgen Barth, is a Porsche man. Maybe that is why the whole work reads like a publicity brochure. A little light criticsm of earlier models is allowed. For example the 912 (1966 - 1968) "was never a car to which superlatives could apply". Description of current cars is the company's line. I havn't found any juicy little titbits of gossip either.
I guess, partly because of its price, this work will be bought only by those with a special interest. They will be pleased to have it but, like me, will wish for a little more.