Thanks! I’ve signed up to try it in parallel with hnreplies.com. I like that this one supports post comments as well.

FYI, the online tool to test without signing up (https://hackernewsalerts.com/view-comments-replies/) didn’t work for my username.

EDIT: Perhaps that was an apt warning. After signup I received 20 updates for comments that weren't mine. Possibly leaking the usernames of other subscribers to the service.