The Humble Book Bundles vary in quality depending on the publisher. I am only really interested in technical topics and have bought bundles by O'Reilly, No Starch, APress and Make. There have recently been bundles from Manning and Prentice-Hall which weren't in my sphere of interest. O'Reilly and No Starch books are excellent with APress not quite as good and I avoid Pakt completely.Welcome to the Clud Bob, how is the reading bundles from Humble. I've been on the verge of picking them up a few times, do they just send you the raw text file that you can read anywhere?
The books are downloadable in drm free pdf, ebup and mobi formats and you have access to all past purchases. I tend to use pdf on an iPad with KyBook reader and the experience is excellent.
There are regularly bundles from the same publishers and they often include repeat titles but can still be worthwhile.
I have just bought the 'Learn You More Code' bundle and although I have many of the books from earlier bundles it was well worth £12.90 for those I don't have including Effective C which is currently £23.74 on Amazon for the Kindle version.
From my own experience I can highly recommend these book bundles.