Hi Gr...I have both the Cera and Luna.
Luna's side switch is much more convenient than the bottom switch on the cera. It has a nice feel with a good amount of 'pushback' (to prevent some accidental firings). I do wish the switch itself was a slightly different material. IMO the delrin switch seems "cheap" when compared to the materials that make up the rest of the unit. All in all, much more ergonomically appealing.
Yes, I would say the Luna is both noticeably lighter and shorter (at first I was shocked at how light it was without the battery). However, once the switch assembly is fitted for the Cera body, the overall length of the two would be much more comparable...(<1/2 inch difference I'd say). In my experience, the ceramic handle of the cera, because it surrounds a portion of the cartridge, will do a better job retaining heat once warmed up. I am still torn as to what my ultimate preference will be, Cera with an improved switch, or the Luna.
Oh, and no experience with the liquid cartridge...sorry.
You helped a lot, thank you. Still on the fence, the luna liquid cart is set up at 7.4 volts and seems that is an improvement for speed of vapor in the ejuice world. Still it might make sense for me to get a liquid cart for the Cera just to see if it is something I will use or if I am better off in the ecig market for my needs.