Hi, Leonid:)

1. We do need counter, it shows us how many messages we have in "unread" status.

2. It is good idea to be able to reset counter in case of mass-chats, , for example in  popular posts comments chat . I don't want to read (and even scroll)  aaaaall of this, want just  "mark as read", as we do in e-mail inbox. 

3. To be clear: I'm talking about good-to-have option which is FB-standard. If (IF) UNA devs sometime, somewhere, somehow will aim the counter improvement - it will be very appreciated :)

Good day there:))