I've not gotten to duals yet in these, but have played with plenty of RBAs to have found a few basic rules. Smaller chambers give better flavor and seem to often enhance sweet notes of the flavor. Duals can produce massive vapor and go through juice faster. If you get enough air flow, think direct lung hits, dual aren't throat burners but because your vaping a lot more juice can produce a nic buzz quickly.
Part of the problem with comparisons is most people go to a lower ohm with duals and this has an effect on flavor, it can shift it and they sometimes attribute the shift to the RBA and not the change in coil ohms. So my first test is with the exact same coil and ohm as I run in my Chalice, Cyclone, Divo or RM2.
So far with a single coil the RM4 has better flavor than a Odin but not as good as an RM2, this is what I would expect with the larger air chambers. Over the next few weeks I'll test with lower ohm single coils and dual coils.
A dual coil RBA wide open airflow with that 18mg NT juice on Wedding nights might really hit the spot.