Haven't done it, but thought about it. A lot.
I don't recall all the specifics, but the DMsGuild conversion may have been related to a crowdfunding campaign that was IMO pretty shady. I don't think the results were shady -- it wasn't a "take the money and run" scenario IIRC -- but rather that it was run in a way that didn't at the time strike me as understanding how copyright works. Mostly just a personal feeling of "this is weird" so I ultimately stayed away from it. YMMV
So, I took a look at doing it all myself and figured it shouldn't be that hard, relatively speaking. This is how I would approach it; there's a TL;DR version at the bottom if you don't want to see the specifics of each step.
First, find all the more-or-less 1:1 swaps you can do using 5e monsters as-is. Given that you can reference 5eSRD.com (or DnDBeyond, or your favorite variant of choice such as Level Up's website), there's actually a lot more 1:1 swaps than you'd think if all you have in your brain during that phrase is the Monster Manual. In short: there's a bajillion monster stat blocks freely available out there: use them. IMO, just build a list with links to the 5e versions and you're mostly done.
Once you have that list -- something that'll probably take 30 min to an hour to compile, unless you're completely new to 5e, in which case maybe a few hours to compare stats and whatnot -- most of your work is done. You'll do the same thing for magic items but there's WAY more that are available as 1:1 swaps. Like pretty much everything. RHOD of relied on the core rulebooks for rewards, so you're work is basically done with a simple list and/or a list of links to the 5e versions.
What you end up with after a few hours of compiling is probably a list of a dozen or, at most, two dozen things you really need to convert "from scratch." But why work harder when you can work smarter? At this point in the conversion process, you can actually stop worrying about specific stat blocks (for monsters or items) and start combing through what you've got to benchmark some encounter level guidelines. I woudn't go encounter by encounter, but rather pick a set-piece or two from each chapter (since that's the bulk of what RHOD is anyway) and see what you come up with using the list of 1:1 swaps. Yeah, you'll find some of the "not-yet-converted" monsters in these encounters, but in that case, just see what you come up with without them, and then think about what levels of PC parties you actually enjoy running games for, and see what shakes out. You'll probably be surprised to find a lot of interesting things doing this. Things like "do most encounters cluster around a certain difficulty level for specific levels" or "are there some encounters that are grossly over or under what your expectations are or what RHOD suggests the appropriate level should be at this point in the campaign." Given how relatively vague and perhaps overly simplistic 5e's encounter guidelines are, this process should actually go pretty quick: find a tool like the Kobold Fight Club tools and just plug in the monsters or equivalent Challenge rating ones versus expected levels and you're done; takes like 10 seconds per encounter.
And that's when you make your decision for what levels you want the players to start at, whether you're doing milestone or XP leveling, and now it's just a matter of cutting or adding monsters to massage the encounter levels. At this point in the process, you'll almost certainly find it easier to drop the weird outlier monsters and/or sub in stuff that's already existing in some source so you don't need to convert things.
Then you're at the final stage: whatever's left over, convert that. Like you'll probably need to do a little work on the true Big Bads of the campaign, but there's really only a couple, and the best part is you know you won't need them right away since they don't appear until later.
TL;DR: Compile existing stat blocks for monsters, and existing magic items from whatever sources you have available. Then use a quick encounter difficulty tool to benchmark where you want the PCs to be in terms of level and difficulty. From there, you'll have a list of conversions you need to spend more detailed time and thought on, but in almost every case, you won't need them until your further into the campaign, so only put in the work if/when needed.
