Apologies for some formatting nonsense on my part below--what I wrote vs how it looks on the site are two different things, but it should be comprehensible nonetheless. [I've added a brief response to Mark below since I don't know how else to respond to it save by editing this.]
For whatever reason all of Mark Stout’s guides to the U-series have a blank second page—I’m not sure if this is padding or a formatting problem, but it’s annoying. Speaking of padding, the information contained in pages 4-8 is subsequently repeated on 9-10, so it seems like the actually substance of the pdf is just 4 pages.
Let’s ask some fundamental questions that I have for any conversion: Does the document discuss the plot of the adventure? No
Does it go over potential pitfalls or special elements within the adventure? No. Does it offer any advice whatsoever? No. Does it explain the conversation process? No#. Does it explain the replacement of monsters/items? No%. Does it include custom monster equipment and explain why or why not it was included? No. Has it been updated with subsequent 5e releases? No@. #There is a free pdf which does, but it’s odd to not at least discuss it (I mean, there’s a blank page included—might as well fill it with something). % For example: why does a Ring of Protection become a Ring of Jumping?. @ For example: Aquatic Elves are now Sea Elves
Not going over the plot is particularly egregious because the events behind U1 are only fully detailed in U2 and U3—you cannot, as a DM, know what’s really going on in the series without reading those books (and knowing informs your decisions).
The only suggestion included in the document is one that’s already inside the original adventure itself: design the town (albeit without the specifics from the original included, even in summary).
There’s a big difference between AD&D (1e) and 5e that I think is glossed over here. For example: what good are spellbooks to Sorcerers or Warlocks? What does a DM do about 5e races that can either breathe water or can fly? What about the impact of PC’s gaining five times the magic items in a system that you can play with none? What about the assumed language barrier throughout the series which is minimal in 5e? It goes on and on.
This isn't to say the product doesn't have its good points, it's largely suffering from what it doesn’t have. What are the positives? Price, certainly, but what about the specifics? What does the pdf include? Random encounter tables (as found in the adventure). A list of all encounters by room.
Updates for traps and skill checks (DC’s etc). A list of magic items (with updates where necessary). Updated spells (when necessary)
What you are getting is a time saver, but of a very specific kind. This pdf will serve you best if 1) you already know the material, but 2) are short on prep time and don’t want to have to review it. It’s a quick & dirty, combat-focused document that you can have at the ready to ignore the old 1e stat blocks when you run into them.
For anyone new to the adventure, however, it isn’t going to save you that much time. You still need to go through the adventure and figure it all out on your own (and in that process, you might have your own ideas about how you to convert things). There’s no comparing this product to, say, Sean McGovern’s supplementary material (which is filled with advice and solving problems from the published source). This is not a product that is going to help you understand the material at hand, it’s purely for running the adventure as-is.
[Mark's comment that explaining his process would be boring is a little bizarre--how can someone buying the product judge his decisions if they don't understand his rationale? It forces you to reverse engineer what was done and then figure out if those changes are ones you like, which means you didn't need the document in the first place since you're already converting work (figuring out the monster switches in the U3-conversation was a pain in the ass--adding time to my work rather than saving it).
[The Aquatic Elf explanation I don't understand at all--nowhere else have you substituted 'nomenclature' when a 5e variant exists. It feels like you simply didn't update the document once the Sea Elf was added.
[I appreciate the explanation for the blank page--although it's a very odd formating quirk to maintain. I'm well aware the latter two pages are intended to be easy to print--my broader point is simply how little content you've included (your intent isn't relevant, it's to let people know an 11-page pdf is really just 4 pages of content).]