I checked my profile by visiting old.reddit.com/user/[username]/comments.
Then I used shreddit to edit/delete my comments, and kept viewing that page to confirm comments were being removed. I also picked a handful of comments and confirmed they appeared as “deleted/removed” in the threads in which they appeared.
When shreddit was done, I checked my profile comments list to confirm it was empty. I double checked 1 and 12 hours later in case there was some cacheing.