FWIW I know there are a bunch of other "HN notification" sites. dang has previously commented why he doesn't think this feature fits with the ethos of HN: https://news.ycombinator.com/item?id=27901918
Not a fan of this for aesthetic reasons. I enjoy that HN is beneficially slowed down by a lack of notifications. I believe it is a valuable distinction from most other forums and mainline social posts.
It's useful to have options. In particular, I prefer RSS/Atom feeds (polled once a day), rather than visiting Web pages to check for updates "manually". HNReplies lets me treat comment replies in the same way (I'm currently consuming both in Thunderbird; in the past I converted RSS to maildir and consumed both in Emacs).
Also for the privacy conscious, hnreplies had a data breach in 2021, making public the link from email address to HN username: https://news.ycombinator.com/item?id=26968908