We looked at something like this.
One thing that comes up almost immediately when the service does *not* use fiber or conventional interconnections is how far apart can you get the users.
They don't appear to address this, but I'd be surprised if you could separate the users more than about ten feet or so. That means everybody's in the same room.
Are you *really * good friends with the other editor? Anybody cutting sound yet? Anybody have a pet snake? Anybody like talking on their cells while they edit?
Koz