Great contribution to the community, thank you for the work!
Here's my dumb question: exactly how do you use this in your game? On a tablet, skimming up and down for stats? Or keep the MM open for one thing while this document is open to another?
The document seems promising but I'm not sure how to use it to good effect.
Not a dumb question. Unfortunately, unless I completely reproduce the MM (something I'm not willing to do for the reasons stated above), you're likely always going to have the MM in front of you (unless you're running a published adventure with the stat block in there). In the worst case scenario, let's say you've got a bunch of stone golems accompanied by the lich that created him. The golems are run from the MM, and the lich is run from my doc because it lists out the spells (the creature's powers have NOT been changed). The lich's stat block is two full pages, so it's one of the most unwieldy of the blocks I created (but totally worth the complexity because that lich as written is very powerful and a fun challenge for the PCs).
What you'll have to do is have the MM (or relevant source book) sitting on your lap, then two pieces of paper on the table in front of you. The reason I started this project is because, and unwieldy as that may be, that's much better than having a MM on your lap that you must jump through between the lich and golem entries, and another hardcover book (the PHB) that you must thumb through as you're going from spell to spell on the lich. Is the first scenario perfect? No, but it's seemingly infinitely better.
The scenario I described, however, is unlikely. Most of these two-page stat blocks are for creatures that can absolutely stand alone, so you can create interesting and memorable encounters that can be run without the MM sitting on your lap. On the other hand, if you're using my couatl stat block, you still have the scenario I described above, but the unwieldiness is reduced because the couatl is only one page, and if you're using a small tablet, it doesn't take up much space at all. Off the top of my head, the only exception to these caveats (there may be others) are the Drow Mage and Drow Priestess. These are not legendary creatures. They'll almost certainly have allies with them, yet their stat blocks are over a page long. Still, this is better than having two hardcover books on your lap, thumbing back and forth through each depending on initiative order and what spell is being cast.
I hope you can find a use for these that works for you.