My main concern is that it may not have history facility. The great thing about phpBB is that you can search the archived posts to find stuff. Does this support that sort of feature.

Also Flash is a 3rd party add-in.

Due to the diverse nature of timezones, I'm not sure having it will provide that much extra to the site. I would guess that anyone who wants to chat some someone privately either use the PM fearture or use one of the IM clients ( ICQ, Messenger, Yahoo etc ).
My vote is currently Unsure, until someone provides more compelling information.