Might depend on which RCBS model you're talking about.
I have the RCBS Uniflow and I like it a lot but I'm sure there's something better out there. I use THIS
that mates the Uniflow to my Lee powder through expanding dies. I use an ancient Lyman beam scale to set up the Uniflow and to check the drop once and a while. The Uniflow has a bunch of accessories like a micrometer adjustment and metering baffle. There's two sizes of drop cylinders.
I have a Lee Auto Disc on my turret. Works pretty well but is not as repeatable as the RCBS and not infinitely adjustable unless you buy blank aftermarket discs and drill them yourself.