By seeing your post date I think you must have started writing reviews by now. But still if you have not done so, then I will like to answer to your query. If you are talking about any formal permission or approval to write review then as far as I know one does not need any formal permission to write review in IRC. But all the review will be published only once they are approved by the admin / webmaster. I joined some days back and I started writing review straight away (though they are pending for approval till now :)).
So, jump in and contribute your knowledge about various product here just in case you have not started.