I did the same as you, initially reach router seemed like a great alternative, but it really doesn't feel finished, updates are few and far inbetween, and there is a large backlog of open issues / PRs.
Yes, these type of services help get around the headache of supporting multiple platforms / versions of the same platform, and their different notification APIs.
Sessions are the killer feature for me. I have a session for each project I work on and can have all my tabs, panes, vim, etc set up and switch between them at any time. Sessions can be persisted so that even if I reboot my machine all my project workspace configurations are saved and ready to go.
> If a user denies the notification request then the site is never allowed to ask again
Sites will start doing what apps have been doing for a while on ios, use a custom dialog to ask for the permission until they agree, only then will they trigger the native, one time only dialog.
There isn't a compelling reason imo, you get a dark console theme, slightly nicer / slimmer browser chrome, and a newer version of FF than the normal stable release, I'm not sure much else is different though.