It does work in deleting comments properly (i've tried other extensions that only superficially delete commets). This deletes comments on the old overview page of old reddit. However it times out. And I get this error:

Looks like there’s a problem with this site
OLD_REDDIT_URL sent back an error.
Error code: 429
Check to make sure you’ve typed the web site address correctly.

if this can be worked around then that would be good.