Tomas - I bought three of the would-be "ultimates" a couple of years ago, all around EUR 60 delivered, give or take a few. You get a lot of weight for your buck (or Kronor). There is definitely some very useful stuff and some quite interesting reading. The industrial action background in the A-20 book was highly interesting, as things like that rarely get mentioned. OTOH, I have a bit of knowledge on the Boston, and did spot a couple of errors in the British section on a casual read. In addition, one of the chapters is essentially a technical manual spelled out word by word. Which I consider pretty pointless. The long introductory section in the B-26 book is interesting as it gives a lot of background to Glenn Martin, but somewhat culminates with a lengthy discussion of the groundbreaking question "was Glenn Martin gay?". I did not dare read further, and the B-25 title remains essentially untouched. You will certainly find lots of useful stuff, but to me the books look like a (sometimes rather incoherent, or somewhat random) collation of mostly secondary-source information, apparently many drawn from contemporary aviation mags.