I have the 350 with the lens support but can honestly say that you probably won't notice a difference using it with/without. If you have RRS plates (as I do) on my RZs it necessitates taking off the plate, attaching the support to the body, and then using a separate plate to put on the bottom of the support. In short: a pain.
If you don't use plates on your RZ than it might be worth it for you, but I find myself rarely going to the bother.
Andrew.