Wall warts are just the power transformers that turn 110AC into 3v-12v~ DC. They are the big honking things that take up two to three AC outlets on your pwerstrip cause they are so big, thus the name wall-wart. Companies use them for several reasons but the highest on the list is they use off the shelf wall-warts from other companies that make them so they don't have to get UL certification for their own power supply. And they can make smaller boxes since the power transformer is external. But then we have to put up with making sure we have the right wallwart for the right piece of gear, our power strips are over crowded, etc. So yes it is nice not to have to deal with wall-warts, but it shouldn't be a deal breaker.
Now, I have never tried a RNC but I do have a PRO VLA. Here are my uneducated thoughts on the two. First the RNC supposedly does clean compression (some might say to clean), where the PRO VLA adds character (some might say thats just distortion they don't want). I feel, again since I have the VLA and not the RNC here comes the biased report, you can get clean compression in your computer all day long from software compressors, its harder to get character out of software compressors. So I would and did go for the PRO VLA because of its "mojo". Your needs may vary.
EDIT: they beat me to the wall wart explanation, cause I went to go eat breakfest before fininshing typing my reply, it was pancakes, sausge, and bacon...