One of the problems with e-books is the transfer process from print often garbles data--a problem not only withloading manuals but cookbooks, the main reason neither Gun Gack or Eileen's cookbooks are available electronically. It would take WAY too much time to make sure all the numbers come out right--which of course drives the price up.
That's the main reason I tend to go for PDF formatted stuff when I download the old stuff. My iPad supports both. With Kindle formatted classics you never know what you're going to get; text jumps all over and images get futzed up too. The PDFs are really scanned copies of originals, complete with creases, library markings and boogers stuck in the margins. The Selous books I downloaded the other day even had the nifty embossed animals on the covers.
The Kindle stuff I get from Amazon is usually of very high quality, but generally ain't free either.