Regarding AAU:
Yeah, the latest public release on Github for some reason didn't include the installer batch file. I'm uncertain why this is the case. When I did it, I poached the batch file from 1.7.3 and used it to install 1.9.1. In cross-checking it against other releases, it seems the code for that file tends to not change between versions, so I would assume it's got a lengthy list of compatibility, both forwards and backwards.
With that said, support for trying to run the original AA2 is for the most part non-existent. Almost all guides and instructions, including those for applying AAU, seem to assume that you are running AA2Mini. When I tried applying AAU to the original AA2, it mostly broke my game. To this day I do not know exactly what it does that breaks the client, but frankly, it's probably better that way. AA2Mini is simply that much better.
Regarding AA2 vs AA2Mini:
For the most part, it is what it sounds like. AA2Mini seems to retain most, if not all, of the functionality of the original AA2, but highly compressed. It's also substantially more user-friendly to mod, too, which is a nice touch, and it also comes with a myriad of pre-applied scripts to for you to use to optimize and customize your gameplay. Of note is that all of the pp files from the original game's data folder have been centralized to a single file.
Currently, there are two versions depending on the type of encoding used: PP2 and PPX. The download in the OP of this thread is for the PP2 version, which for the most part has lost its community support. A link to the PPX version can be found in the
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. Whichever one you use, you'll want to make sure that any mods you apply follow that convention: AA2Mini (PP2) can only take pp and pp2 files, while AA2MiniPPX can only take pp and ppx files.