So I've been using Rainviewer w/ Annual Subscription since they launched their new version (June 2020?) - for a couple of months now.
It's good, when it works. I've tested in China for a month, and it was a mess that couldn't be trusted, ever.
I'm now using it in France and it is better, predictions are better.
BUT, the 'upcoming precipitation' section is simply bad. It doesn't work consistently.
Notifications are a little bit better but you may encounter precipitation notifications that won't show in the 'upcoming precipitation' section.
In short, it cannot be trusted solely based on notifications nor 'upcoming notification' section. It does offer worldwide coverage, but quality will differ, greatly.
Although, it looks very promising and I hope to see signifiant updates that will solve those issues. Hence my rating of 3/5.
I should say that I have contacted a few times the developer on different occasions to discuss previously mentioned issues. I did get reply but no follow up, not ideal but again, promising.
Good luck to the dev!