I was trying to get it to work on 3.4.1 and although it lets me apply and be granted acces, there's no way to save the access once granted. The "Forum restrict administration" has no save button, so when you leave the page you still have no access. Also, there's an un-named tick box on the far left which, as soon as you clich it, deletes the record its next to. And then you need to start again.
The other problem I see is that it identifies a user based on the IP address. Which is OK if you're on a fixed IP, but if you'r on a virtual IP from your ISP then you get a new one pretty often. As a result your constantly having to apply for permission.