The more I look at it, the more I think that the whole sentence is a recommendation. They could have made it clearer by reiterating the 'recommended' word in the second part of the sentence, but probably thought it was overkill. Certainly, if the 500/600ft rule were mandatory, then it could have been written to indicate this as demonstrated in my previous post.
I think the 1800m RVR is definitely mandatory although I can't find the reference to it in the AIP.