technically you can't trust me, but the code is right there and should be easy enough to understand so that you can verify im not doing anything shady. otherwise "trust me bro"
My answer (like OP's one) is:
You do not need to trust (blindly like for closed-source or platforms). The script is FOSS, you can check every step it does, before you use it. One of the biggest benefits of FOSS :)
I would recommend making a full git repository and at least adding a license header so that others can expand upon it. Maintaining a useful gist is cumbersome as issues tend to be ignored comments.
you can also export everything (posts,comments,etc) on reddit via the GPDR data export (assuming its available where you are, idk if its only in the EU)
oh yeah, you could also just paste the multireddit URL into a text file as a backup for now. that would do it. there is nothing fancy or time-sensitive in it, literally just the sub-names