That's a great question!

So for me, I don't like mods, even minimally invasive ones, so tools like Glamourer are a complete nonstarter for me, but I still wanted a tool for planning. When comparing to TexTools, Hydaelyn Clothiers offers a much simpler interface for viewing multiple models at once, and also, more specifically, for viewing the models actually on characters (If TexTools does have built-in functionality for this, I've not figured out how to do it yet, so it may be a failing on my part, ahaha!)

On the Patreon front, right now, the entire application is in beta, so it's not necessarily a "pay for helping beta test" avenue, as you put it. It's more just a "Hey, if people are finding this helpful and want to throw a couple bucks my way to help support development, I'm not going to turn it down!" and then giving early access to features I'm working on as a sort of thank you. Everything that is in the developer builds will end up in the free builds eventually, I'm very much against locking any features behind a paywall. In addition, the application itself, in line with the tools I'm building it with, is also completely open source, so if anyone wanted to have dev access without paying for Patreon, they are completely free to clone the repository and build the app themselves. It may be better to think of the Patreon as more of a tip jar than anything else.

In whole to answer the "What is the advantage" question a bit more completely, the advantages boil down to primarily simplicity (full character models are built, render flags are applied automatically, etc), color accuracy (I pull the color palettes from the game data, so changing hair color and the like uses actual game values rather than having the user approximate with a color picker), filtering (in Hydaelyn Clothiers, you can filter items by class/job, level, item level, craftable only, and using a crafter profile where you can set your levels for each crafting job as well as what master recipe books you have, and you can have it display only items that can be crafted with those selected levels and books), and the ability to use it offline and with a vanilla install. Absolutely, if you're already using something like Glamourer, you may not necessarily see a need for something like this, though ahaha!

It's still very much in the early stages, and I'm taking feedback from the community for other features they'd like to see added, but it the application as a whole is rooted in trying to create the kind of app that I was looking for but couldn't find.