I know i can just read the code, but i'm not skilled enough with windows to know if there's something else snuck in there or not.
I think that in this particular case you can trust the random bat file more than Microsofts official binary blob OS.
Aside from the obvious risks of downloading and immediately executing internet code, which are indeed risks but of course we all accept them on a regular basis...
... and aside from the mildly more subtle risks that the HTTP server is doing something sinister, e.g. with browser-agent, and so you're not getting the code you think you're getting...
... even aside from these issues, curl-and-pipe-to-sh is dangerous because of its failure modes.
There are blog/post links in various comments in these files, I should note.
I'm not sure how documentation would help with the "might sneak something in" issue either. If anything, if you're feeling paranoid / reasonably cautious, you should ignore the documentation in favor of documentation you source yourself - if you can't trust the author to write the commands, you can't trust the author's documentation of the commands either.
The solution is that someone trustworthy vouches for the files.