I'm so glad that someone built this. I have the same use case as the author where I just don't want newsletters to read, but that are time insensitive, intermingled with communication to people in my inbox. I'm excited to try this approach.
I'd be interested to see what other solutions people have come up with to this problem.
A simple approach is to filter them in your email client into a folder/tag and out of the inbox. That's what I do for mailing lists (which aren't well suited for RSS, since they're threaded).
That's what I do today but what often happens is I just never check them. Also some newsletters contain events or occasional time sensitive bits so partial filter has proved a challenge there. Curious to hear if you've experienced either of these.
I used to also filter them out to a folder with no unread tag until I realized that I missed quite a few free ebooks that O'Reilly was offering. Since then I still have them in a folder but I go mark it read once a day to make sure I don't miss stuff like time-sensitive offers.
I'd be interested to see what other solutions people have come up with to this problem.