Aha, so there's the difference! Whereas a UC style RDWC recirculates water sequentially through growing sites before sending it back to the 'epicenter' to be oxygenated and sent on, an mpb gets reservoir water directly to each site. The apparent complexity is more about redundancy, fair enough.
As it happens, I'm headed this direction as well; the RDWC- or maybe it's now an mpb?- under my vertical cylinder grow experiment consists of two black 27 gallon tubs draining through one 1" bulkhead each to a tailbucket, aka 'reservoir'. Even if it's only a 5 gallon bucket, this is where the pump drives water through 1/2" lines to waterfall back into each tub. In this way, I plan to dispense with an air driven aeration system altogether. The waterfall should agitate and oxygenate the water inside the tubs just like it does in an epicenter- it always annoyed me that the best looking site for plants in a UC was the only one you weren't supposed to put one in!
My current plan is for one 1" outlet near the bottom of the tub. If it becomes an issue, I could drill a second one either next to it, or up higher so it could serve as a drain- I like that idea. This is starting to sounding a lot more mpb-ish, isn't it? The 5 gallon tail bucket would have the pump submerged in it, and this also isolates debris where I can see it. The cooling coil to keep temps down also lives in the tailbucket, where circulation, and therefore heat transfer, is highest.