I used that one to delete my comments and submissions, but when I did a search of my username there were some that it wasn't able to delete. Turns that for those the GDPR data reddit sends you needs to be used to go through and delete those comments individually. Haven't had luck setting up shreddit so been going through the permalink provided in the data request and deleting it one by one.
It's mixed in with data that was successfully deleted, so in 30 days I'll request another one for a more cleaned up list that only contains the undeleted material.