I have been looking at a RAS (I was looking at the new ARMS RIS, but a lot of people have been saying it is not that great) for mounting a light and possibly a vertical grip.  Any advice on what type of RAS to get (if any) would be appreciated.  Also, do the plastic covers for the unused rails insulate your hand from the cold or heat of the aluminum?  
Thanks.

[Edited because I need to F-O-C-U-S better]

Is it worth it?  Well, for us who are not "operators", its hard to answer that.  It was worth it for me.  The quality and workmanship are top-notch.  But it is pricey...  I guess it comes down to are you going to use it?

As for the heat issue, having owned a V-match (aluminum handguard) and now a RAS, I can say this is not an issue.  I can only imagine the kind of sustained, heavy fire it would take to heat up the handguards on either of those to a point where it became something you cared about.  Winter?  Well, if its THAT cold, you are probably wearing gloves anyway.  I would say this is just simply a non-issue.

Thats a sweet question, I too would like to know what people think. I do like the idea of "free floating" the barrel, cant hurt accuracy any! Yes 300 bucks is pricey just to attach a few things. It would be worth it to me just cause it looks Bitchin!!
            Foldemfast

Yeah, floating the barrel is one of the main reasons I like it, too.  

Knight's RAS's, except a few that were recently available, do NOT free float the barrel. MSTN and others have some that do, but they are more expensive and are very limited in qualtity available. I have a standard non FF RAS and like it a lot. If I'm pulling it tight with a sling, it's probably not my M4gery anyway....