I was thinking of investing in one of these for my M4gery.  I currently have a Fobus M44 and I'm not happy with it.  I don't feel the need for a free floating handguard, thus I was thinking of these two options from Knight's.  What is the main difference other between the two (any size, weight, or mounting differences)?  Users of both - please sound off.  I would like to hear the good and bad points about both?  I was also wondering whether the extra bucks is worth it for the Knight's or whether I'd be just as happy with the less expensive Surefire M73.  I've seen some RIS's available for sale from some of the dealers, but no RAS's.  Oh yeah, one more thing...why is the RAS II cheaper than the M4RAS??  In looking at both, I would think the RAS II would be more expensive

I bought an excellent condition RAS from a guy for a little over $200 and have been very happy with it. I like the KAC RAS design and the fact I had one on an issued weapon so I was familar with it. Would I have been happy with a Surefire M73?? most likely. I just wanted the RAS. I put a vertical fore grip on it and a light. I like it a lot. keeps the heat off my hands. I like the rail covers. I think they are well made and fit tight.  Easy instal (less then 5 mins) with a locking clamp that uses an allen wrench. I have yet to see any drawback on this rail. 1000's of them in service with the Military.
Probably the only drawback I see is the price of the rail covers. they are not cheap, but that problem can be solved with a plethora of after marrget rail covers from Magpul,TangoDown,etc.

I have an HBAR and the RAS fits it with no problem. The RIS is pretty simular. First generation to the RAS (But don't hold me to it). as to freefloating. not a big need on a carbine 300meter or closer weapon, that's my belief based on my experience and the performance I get out of my weapon based on my skill set.  Honestly with all the newer rail systems out there and everyone buying them. I would be looking for a deal on a RAS or RIS. I have seen them for $200 which is pretty close to the price of a surefire. And KAC is pretty much the standard for non free floated rails. That is just my opinion. But based on what others have posted with Surefires, I think you would  not go wrong with one of those either.