Are you certain they're not a good Photoshop job?
I am getting confused, are you after a real, working RDA ?
I was just speculating as to why the RDAs might appear to be so big. I believe the OP would like a real, working one, if they do exist.
From my experience, the bigger the size of the RDA, the more your flavour will suffer. Of course if we keep the coil size the same.
I wouldn't think there is any benefits to have a 30 mm RDA except for experimenting with coil builds. Building a SSFC with 24g/0.5 is much easier than 28g/0.3 initially until you get the hang of it. Then you will be back to the 24s and 22s again.