Value Proposition
You mentioned DDI:
Even better is the WotC approach with the DDI, you can look up any
monster or item or (almost any) rule, in the most recent form, for 3
years at the cost of seven books. I think this is the way to go, even
considering the horribly slow character builder.
It's true, for three years that is a good deal. But what about for six years?
I'm still using my 3.5 PHB, ten years after I got it. I have a set of 3.5 books that is nowhere near the full quantity they released, and I'm okay with that because I don't care about a lot of the books they put out.
If DDI existed for 3.5, it would have cost me more than I paid for the books rather than less. Being an upfront cost, books don't cost more if you use them for longer. Subscriptions do.
And of course, online services disappear every day. Will DDI for 4e still be around in 10 years? If you want to play and it goes away, where did your rules go? I own a book from the 1800s, so I'm pretty confident that Wizards can't take my 3.5 paper books away should they decide it's time to move on and not pay for servers anymore (or go out of business).
Page Flipping & Sharing
I have bookmarks in my PHB & DMG. I also just know where some things are, because I've had to use them so many times. I can open the book and be in the grapple rules in two seconds. No matter how hard I try, I can't get there that fast on my iPad. I also can't have the grapple rules AND my encounter notes open at the same time with the electronic version, since my iPad can only show one thing at a time. With the books, I can put them beside each other. I can then also add a spell description from the Spell Compendium. The area around me when I DM tends to look like a book fort.
It's easy to share the book. I can hand someone my PHB so they can look up a spell description and keep doing what I was doing with my other books & iPad notes. If I have to hand them my iPad, I just lost access to everything until I get it back.
Subjective Stuff
There's a subjective side to this as well. I like how books feel. I find them easier on my eyes than ebooks. They work at the cottage, even with no power.
In the end, it's really about which trade offs you prefer to make.
It is a D&D 5e-compatible adventure by Troll Lord Games. They're most notable for being the publisher of Castles & Crusades — and being Gygax's last publisher.
The odd numbering system is how old (1st edition) adventures were numbered - and while I can't attest to this, I believe this is a series of 5e compatible adventures with an old-school feel.
You can click on Troll Lord's link on the site to see their available catalog.
When you ask if anyone knows what these books are about - I am not sure if you mean either of the following:
- What is the narrative content of the adventure?
- Are these books (un)official 5e material?
While I haven't played any of TLG's 5e-compatible content, I did run Goodman Games' Into the Borderlands, their official 5e conversion of Keep on the Borderlands, for almost two years. 3rd-party content quality varies by author and publisher — but much of it is very good. That book was beautiful and was a blast to play.
I think you'll find quite a bit of people out there who heartily endorse 3rd party content.
Best Answer
It's the Dungeon Master's Guide
In this case the "Ultimate Book of the Master" is just a playful reference to the DMG - since that is, after all, the book meant for the "master" of the game. A lot of the published material of that era seems to refer to the DM's position and authority with a (possibly tongue-in-cheek) reverence which feels quite out-of-place to my modern reading, but oh well.
Page 115 of the 1st edition Dungeon Master's Guide is indeed where you can find the rules for independent spell research, and that was the current edition of the game at the time Dragon #82 was published - 2e didn't come out until 1989.