Nice book, that I have not seen before. Great find. No idea on the website, though the literature advertised all looks genuine and they offer a guarantee that things are "genuine unless otherwise stated".
I have had some dealings with the gentleman behind the od43.com website and found that he was helpful and knowledgeable.
The book itself isn't super rare - various copies are available with other dealers: BookFinder.com: Search Results (Matching Titles)
I don't know if you are in the US or Europe - obviously that will have a big effect on the cost of shipping. I've bought a number of original TR books through various German book dealers without any problems.
I've never dealt with OD43 site, and while they have had some nice items over the years, esp. the original books, I must point out that they can be a bit pricey IMO, and be careful with some of the "original rare" documents such as Eichmann and Heydrich signed pieces. As with any dealer, be careful and do your homework before buying.
Your Polizei book is nice btw!