I have had an RNS510 with a Fiscon and MDI, yes you can't beat that OEM feel and it was a nice setup.
However, I also have a Zenec e-2014m (or check the more padded out NC-2015 as it is a better comparison) and these have everything you want built in, and are very OEM...much more than the Kenwood DNX types I have seen up close.
I would say the only place where the RNS510 trumps it is the HDD.