I personally don't have a problem with this feature, and it's actually how I discovered Signal use among many of my friends.
But I think it's inexcusable that these sorts of notifications could essentially allow someone to circumvent blocking done by one of their contacts. If I've blocked someone via my phone's default contact blocking mechanism, and then I join Signal, and that person is already on Signal, they should not suddenly be able to contact me... and even be explicitly invited to do so on their end!
I wouldn't be surprised, though, if neither Android nor iOS gives regular apps access to the blocked contacts list. So I'm not really sure how an app like Signal could solve this problem.
But I think it's inexcusable that these sorts of notifications could essentially allow someone to circumvent blocking done by one of their contacts. If I've blocked someone via my phone's default contact blocking mechanism, and then I join Signal, and that person is already on Signal, they should not suddenly be able to contact me... and even be explicitly invited to do so on their end!
I wouldn't be surprised, though, if neither Android nor iOS gives regular apps access to the blocked contacts list. So I'm not really sure how an app like Signal could solve this problem.