I have fitted aluminum ones to mine. The benefits are that the gaskets for the aluminum covers are far superior to the ones for the plastic covers in that they are quite a lot wider and therefore have a more efficient seal.
Also you can use cheaper aftermarket gaskets without fear of oil leaks unlike the plastic covers which must be fitted with expensive genuine gaskets.
The ally covers have to be fitted so that the oil filler is at the back of the drivers side bank next to the master cylinder, but this does not pose a problem when filling with oil as i use a schweppes(it must be schweppes

) tonic bottle with the bottom cut off as a funnel.
You must keep the breather system clean to ensure that that crankcase pressure does not build up and force oil out of here there and everywhere, there are guides on here that tell you how to clean them out.
some people will try to tell you that if you use aluminum covers that all your oil seals will burst and that you will go to hell, but my advice is to fit em and forget em
