It is a few years since I read on that, so I have no sources ready. As far as I remember the courts decide on cases that are uninteresting outside their respective communities: religious divorce and so for people who are already legally divorced and want to religiously marry again. The courts cannot (bindingly) decide on custody for children. There is not much potential for controversy, which is probably why the courts are so little known. The sharia courts which exist in Britain (oh yes!) have become attractive for non-Muslims too: they work quickly. Under the arbitration act you can take your differences about the plumber's invoice there if the other party agrees to that too. And sharia, developed in a society of merchants, is well able to settle such controversies satisfactorily. (The Guardian had an article ages ago)

I am still of the opinion ALL these religious courts should be abolished.