Andy,
I have all of their stuff. I personally like the RNLA more than the RNC only because it has a bit more of a flavored sound than the RNC.
When I put it on vocals (in my very limited listening experience) they sound older or more vintage than when they are straight. It seems to have a very broad range of usable sounds and effects the levels in a more natural sounding way.
You know, the explanations that Mark puts on the FMR site are just about dead nuts on the money, so I would read there a bit. Mark also personally responds to the emails there so you might want to drop him a note asking specific questions, but my answer to your question is that the unit is A+ for my applications.
So far my two favorite set ups have been SM7 - RNP - RNLA and AKG414 - RNP - RNLA.
Hope this helps.
Jim